1A gap, crevice, or small space between objects; an aperture or crack.
カーテンの隙間から朝日が差し込む。
Sunlight streams in through the gap in the curtains.
窓の隙間をテープで塞いだ。
I sealed the gaps around the window with tape.
積み上げた箱の隙間に小さな虫が入っていた。
A small insect had gotten into the gaps between the stacked boxes.
ドアの隙間に手を挟まないよう注意して。
Be careful not to get your hand caught in the gap of the door.
2A spare moment or short interval (dated usage); similar to 'suki' in an older or literary sense.
隙間を縫って散歩に出かけた。
He slipped out for a walk in a spare moment.
隙間を見つけて手紙を書いた。
I found a spare moment and wrote a letter.
3An unguarded moment or weakness (dated/literary usage); a chink in one's armor or carelessness.
敵の隙間を突いて攻め込んだ。
They attacked by exploiting a weakness in the enemy's defenses.
その計画には隙間があった。
There was a flaw in that plan.