adverbial N4 common casualpolitewritten

大変 — very / tough

大変・たいへん

Meaning

① ①adverb: very / terribly — a polite intensifier, often in set expressions of thanks or apology

② ②tough: tough / hard / a serious matter — describes a demanding or alarming situation

① ①adverb

大変たいへんお世話せわになりました。

Thank you very much for everything (you've done for me).

② ②tough

毎日まいにち残業ざんぎょうで大変たいへんだ。

Working overtime every day is really tough.

Attaches to	Form	Example
Adjective / verb (sense ①)	大変 + adjective/verb	大変たいへんうれしい
Noun (sense ②, な-adjective)	大変な + noun / 大変だ	大変たいへんな一日いちにち

① ①adverb

大変たいへん申もうし訳わけございません。

I'm terribly sorry.

本日ほんじつは大変たいへん寒さむくなっております。

It's gotten very cold today.

② ②tough

小ちいさい子こどもを育そだてるのは大変たいへんな仕事しごとだ。

Raising small children is hard work.

大変たいへん！財布さいふを忘わすれた。

Oh no! I forgot my wallet.

The two senses share one word but split by use: bare 大変 modifying an adjective is the 'very' adverb; 大変な + noun or 大変だ is the 'tough/serious' な-adjective.

Jengo shows 大変 the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.

Sources Compiled with reference to A Dictionary of Intermediate Japanese Grammar.