How to say "largely" in Japanese

• 主におもにJLPT N3approx.Common
  adverbAn adverb: it covers 'largely' in the 'mainly, mostly' sense, modifying the predicate directly. Typical use is saying what something mainly is, does, or depends on; its meaning overlaps heavily with 大半.
  彼かれの病気びょうきは主おもに精神的せいしんてきな物ものだった。↗

  His illness was mainly psychological.
• 大半たいはんJLPT N3approx.Common
  noun, adverbA noun denoting the greater part of a whole: use it for 'largely' in statements about what most of something is. Meaning overlaps with 主に; the choice is mostly structural, not a difference of sense.

For 'largely' as 'mainly, mostly', 「主に」 and 大半 overlap heavily and either word may fit; the practical choice is grammatical — adverbial 「主に」 modifies the predicate, while the noun 大半 names the greater part of a whole.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• 主におもにmainly
• おおむねin general
• 大半たいはんmostly