noun
Refers to a clenched hand. Often used in the context of a fist bump or a punch, such as 拳固を固める (to clench one's fist) or 拳固で殴る (to punch with a fist).
彼は怒って拳固を固めた。
He clenched his fist in anger.
子供たちは拳固で遊びながら喧嘩した。
The children fought playfully with their fists.
拳 (こぶし) is the more common word for 'fist'. 拳固 (げんこ) is less frequent and can carry a slightly rougher or more colloquial nuance, often associated with a punch or a fist bump.
The exact derivation is uncertain. The kanji 拳 (fist) and 固 (hard, firm) suggest a 'hard fist', but the reading げんこ may be a sound shift or a colloquial formation.