na-adjective, noun
promiscuous; loose; unfaithful
Derogatory term for a person, especially a woman, who is sexually promiscuous or unfaithful. Often used in a judgmental or insulting way.
彼女は尻軽だという噂が流れている。
There's a rumor going around that she's promiscuous.
あの男は尻軽で、すぐに他の女に手を出す。
That guy is unfaithful; he quickly makes a move on other women.
na-adjective, noun
Describes a person who is light on their feet, quick to act, or lively. Can be used positively or neutrally, unlike the first sense.
彼は尻軽で、仕事が早い。
He's quick and gets his work done fast.
あの子は尻軽だから、すぐに走り出す。
That kid is so energetic, he dashes off in no time.
na-adjective, noun
Implies acting without thinking, being impulsive or hasty. Often carries a negative connotation of recklessness.
尻軽な判断で失敗した。
I failed because of a rash decision.
彼の尻軽な発言が問題を起こした。
His thoughtless remark caused trouble.
Compound of 尻 (buttocks) and 軽 (light). The original meaning likely referred to being light on one's feet, which extended metaphorically to being quick to act, and later to being sexually loose. The exact historical derivation is uncertain.