noun, noun or participle which takes 'suru'
Synonym of 独り言 (ひとりごと), but 独言 is a more formal or literary term. Can also be used as a suru-verb (独言する).
See also: 独り言
彼は部屋の中で独言を言っていた。
He was talking to himself in his room.
独言する癖がある。
I have a habit of talking to myself.