I've just discovered the verb "to grouse", and while I understand its meaning, I do not understand the difference with its counterpart "to complain". I've looked it up in a few dictionaries around, but most state both verbs as synonyms, and what explanations are given state they can be used interchangeably. I've also looked up the etymology of grouse, out of curiosity, and etymonline.com state the term used to be a british slang of unclear origin. Is there any particular rule regarding the usage of both verbs, nowadays? In what circumstances should I use one or the other?
To grouse is to complain mainly about trivial things:
to complain, often about unimportant things.
as Vocabulary.com notes:
People's excitement about the rise of the Internet has been largely replaced by disappointment that it's turned out to be essentially a forum for people to grouse. No disappointment is too small to grouse about on the Internet. Did you stub your toe? Grouse about it in your blog! Did your sister tattletale? Get online and start grousing. "I grouse, therefore I am," might be the motto of the Internet.