What does grim mean in this paragraph?
I’m reading a book called “Moby Dick” by Herman Melville. The first paragraph of the book is:
Call me Ishmael. Some years ago—never mind how long precisely—having little or no money in my purse, and nothing particular to interest me on shore, I thought I would sail about a little and see the watery part of the world. It is a way I have of driving off the spleen and regulating the circulation. Whenever I find myself growing grim about the mouth; whenever it is a damp, drizzly November in my soul; whenever I find myself involuntarily pausing before coffin warehouses, and bringing up the rear of every funeral I meet…
I want to know what's the meaning of the word "grim" in this paragraph. Someone told me it indicates that he is sullen and doesn't want to talk to anyone. But I'm wondering whether it means that he inclines to say harsh words to other people.