Hello.
If I describe for example the word "collection", should I use "
Collection is things assembled together." or "Collection
are things assembled together."?
In my native language, I'd say "Collection are things..." or "Collection is many things..." but I can't help feeling that every option I've mentioned in English is ungrammatical. Both "Collection are..." and "...is things..." make me throw up.

I know that I can easily avoid this problem by using "Collection is a group of things assembled together." or something similar. But I'd rather solve problems than avoid them. So, which one is correct?
Thank you in advance.