What's the difference between chutney and relish?

It depends on what cuisine it is, though all chutneys and relishes are used as condiments/sides. In European cuisine, chutneys tend to be jammier and involve fruit of some kind. Relishes, like Elendil mentions, are usually made from pickled vegetables. As far as I have experienced, the chutney moniker is used when non traditional ingredients are involved Mango chutney, ginger mint chutney) whereas a relish is used when it is made from slightly more familiar ingredients like dill, cucumber etc (This is with regard to non Indian cuisine).

In Indian cuisine (which is where the chutney moniker originated from), chutneys are thinner and are almost always savory, even when they involve a fruit(eg., mango chutney will have chillies and salt in it). Indian chutneys involve herbs and chillies and sometimes even nuts/lentils. The texture difference comes from the fact that it is usually blended/pureed and usually water based. But then again, you would not have landed in this situation if the meal was Indian, as there is no concept of a relish there.

First, let me sympathise with your excruciating social predicament. However, it really was avoidable, since you are both correct. While there is no official ruling on the matter, it is reasonable to say that a chutney is a type of relish.

The Oxford English Dictionary defines a relish (in the sense of a foodstuff) thuswise:

orig. U.S. A piquant or spicy condiment eaten with food to add flavour; spec. a sauce made of chopped pickled vegetables.

and a chutney:

A strong hot relish or condiment compounded of ripe fruits, acids, or sour herbs, and flavoured with chillies, spices, etc.

So a chutney is a specific type of relish. If I might be permitted to add a personal slant to proceedings, in my experience they are usually a thicker, sweeter, jammier affair involving fruit of some kind, whereas a relish is more savoury.

Chutney is fruit based and has a spicy complexity. Relish is vegetable based and has a pickled profile.

Chutney's originally were and still are made with dried and unriped fruits like dried plums, dried apricots, tamarind, and fresh herbs like mint and cilantro. Each made usually separately. However they can be combined like plum and tamarind with ginger, sugar, salt, red pepper to taste and other spices.They are sweet and spicy at the same time. Sugar and spices are added according to taste. Can be made more sweeter or savory. Mint and cilantro chutney is more savory with lemon juice, salt, ginger or garlic and yogurt if desired. Chutneys have a much smoother texture than relish and have a very tantilizing flavor. I personally like the homemade chutney's way more than the store bought ones. So if you feel like having chutney, opt to make it at home. Get a good traditional Indian or Pakistani recipe from the internet. The word chutney is now used in the english language as well but maybe not everyone knows this word. Maybe that was the case here. I would use the word interchangeably unless if there is another english word for chutney other than relish which I dont think there is. However they are not exactly the same.

Also chutneys are not usually cooked for a longtime. They can be cooked within 5 to 10 mins. My mom makes them sometimes and they are delicious!

Relish can be very similar to Chutney. However, many people think of relish as the pickled variety - dill pickle relish. Your error was in associating Chutney with a non-indian meal. Nothing to be embarrassed about. There is "English Chutney" like Major Grey which is jam-like, or there is Indian or Asian Chutney which is quite different. True Indian chutneys can be wet or dry. They are rarely sweet or vinegary like the English variety. They are considered a complimentary side dish. They may be comprised of spiced fruit, flavored yogurt, spiced vegetables like cucumber, and so forth. They are usually uncooked and finely chopped or blended.

Chutney is cooked for between one and four hours and this produces a smoother, sweeter texture. The food is cut finer to start with. A relish is cooked for a shorter time period and has a more chunky texture and it has more bite to its taste.

Chutneys are lumpier (example: Branston pickle) than relishes, which are much smoother and more finely chopped, in my experience.

Years ago I worked in a Pickle factory and we made Chow Chow and Picalilli (both NZ relish/Chutneys). When a "cook up" was done the cooking vat was wheeled into us in the bottling plant. We were given a pile of Chow Chow Labels and a pile of Picalilli labels. When we ran out of one we used the other labels. SO no difference. Can I suggest you just call it what you want and enjoy it all

Chutney is more spicy and sweeter than relish, which tends to be less "exciting" or "overpowering" in flavour. Both have their place in variety of nice meals. :)

At all times it is safe to call chutney a relish - relish is a more universal term. Stick to it if unsure.

I am from South Africa where we use chutney all the time in a lot of dishes. I find that chutney is sweet - like ketchup but without the tomato taste. You can make chutney from a fruits like: apricot, peach and even tomato. Indian cuisines use mango too. But the common thing is that it is sweet.

Chutney cannot be a type of relish cause chutneys are originated in India. So I'd rather said that relish is a more chunkier type of chutney. Relishes - made from veg, sweet-sour. Chutneys - made from fruits, sweet and spicy.

Clear Pickles

Recommended shelf life: 2 years

Making clear pickles is a traditional way of preserving vegetables which dates a long way back in British history. The vegetables used for clear pickles are often left raw and whole and the main ingredients used are vinegar and salt with sugar, honey, herbs and spices added only for extra flavour.

Sweet Pickles

Recommended shelf life: 2 years

Sweet pickles are a mix of lightly cooked vegetables and sweet vinegar. The vegetables are generally kept in large pieces. Common ingredients which are used to add flavour to sweet pickles are spices such as ginger, all spice and cloves. You can make a slight variation by thickening the vinegar using cornflour and make the most common of all pickles 'piccalilli'.

Chutneys

Recommended shelf life: 2 years

Originally learnt from the Indian colonies in the nineteenth century, traditional British chutney is a sharp, sweet, rich and highly spiced preserve made using a mix of vegetables and fruit which is cooked for a long time. The vegetables and fruit need to be cut into small pieces and the resulting mixture should be easy to spoon and spread.

Relishes

Recommended shelf life: 1 year. Needs refrigerating after opening

Relishes are made from a mixture of fruit and vegetables which have been diced and are then cooked for a short period of time. Relishes tend to be spicy and sweet and sour all at the same time. Relishes do not need time to mature like pickles and chutneys and they must be stored in the fridge after opening.

Note: The above is only one description...(thanks to https://www.kilnerjar.co.uk/a-guide-to-pickles). In my experience people are generally very relaxed about what they call their 'concoctions' - one man's relish is another man's chutney, is another man's pickle. Whatever it's called - just enjoy it...!