功 is used in: 成功 (success), 功夫 (skill/kung fu), 功能 (function), 功课 (homework/schoolwork), 功劳 (credit/contribution), 用功 (to study hard). It conveys effort and its results.
culture
功夫 (gōngfu) literally means 'skill achieved through effort' — it applies to any discipline, not just martial arts. The martial arts meaning became famous worldwide through Bruce Lee and Jackie Chan films.