adverb, noun
mostly; almost; nearly; for the most part
Describes that something is largely complete or mostly the case, with only minor exceptions remaining.
仕事はあらかた終わった。
The work is mostly finished.
参加者はあらかた集まった。
The participants have mostly gathered.
adverb
Used for rough numerical or quantitative estimates; less common than the 'mostly' sense.
費用はあらかた10万円くらいだ。
The cost is roughly about 100,000 yen.
ほとんど is more common and neutral for 'almost' or 'mostly'. あらかた is slightly more literary or formal, and often implies a process nearing completion.
だいたい is the most common word for 'roughly' or 'approximately'. あらかた in the approximate sense is less frequent and may sound slightly old-fashioned.
Compound of 粗 (ara, 'rough') and 方 (kata, 'direction' or 'side'), originally meaning 'roughly' or 'in a rough manner'. The exact historical derivation is uncertain, but the kanji reflect the approximate and partial nuance.