Refers to an amount that can be held in one's arms, or a bundle of that size. Often used with counters or as a measurement.
He brought in an armful of firewood.
That tree is so thick you can barely get your arms around it.
Standard kanji spelling.
Mixed kana-kanji spelling, also common.
Compound of 一 (ひと, 'one') + 抱え (かかえ, 'armful'), from the verb 抱える (かかえる, 'to hold in one's arms').