noun
approximately half; about half
A straightforward compound noun meaning roughly half of something. Used in everyday contexts.
参加者の約半分が女性でした。
About half of the participants were women.
この仕事は約半分終わった。
About half of this work is done.
大体半分 is a more casual, conversational way to say 'about half', while 約半分 is slightly more formal and often used in writing.
Compound of 約 (yaku, 'approximately') and 半分 (hanbun, 'half').