1Words spoken aloud to no one in particular, when alone — thoughts that slip out of one's mouth.
彼はパソコンの画面を見ながら、ぶつぶつと独り言を言っていた。
He was muttering to himself while staring at the computer screen.
「今日は疲れたなあ」と、彼女は独り言をつぶやいた。
"I'm tired today," she muttered to herself.
年をとると独り言が増えると言われている。
It's said that people talk to themselves more as they get older.
一人暮らしを始めてから、独り言が癖になった。
Since I started living alone, talking to myself has become a habit.