Forget about him.
もう彼のことは忘れなさい
forget one's worries at the piano
ピアノを弾いて悩みを忘れる
forget the whole thing
御破算にする
Forget your worries and drink up.
心配ごとを忘れて一杯あけてくれ
forgive (him) his debt
彼の借金を棒引きする
forgive a sin [an insult]
罪[無礼]を許す[許してやる]
Forgive me for keeping you waiting.
お待たせしてすみません(◆Forgive my keeping you waiting. ともいえる)
Fork it over to me.
それをよこせ
forked lightning
叉さ状電光
form (up) into [in] a line
一列になる