へなへな

へ

な

へ

な

Meanings

adverb, adverb taking the 'to' particle, noun or participle which takes 'suru', na-adjective

onomatopoeic or mimetic word

Describes a person or body part lacking strength, often with the particle と. Common in phrases like へなへなと座り込む (collapse limply).

緊きん張ちょうで足あしがへなへなになった。

My legs went weak from nervousness.

noun which may take the genitive case particle 'no', na-adjective, noun or participle which takes 'suru', adverb, adverb taking the 'to' particle

weak; flimsy; easily bent

onomatopoeic or mimetic word

Describes objects that lack firmness or rigidity, such as thin metal or soft materials. Can also describe a person's weak attitude.

ぐにゃぐにゃ
へなへな implies weakness or limpness, while ぐにゃぐにゃ suggests a soft, squishy, or wobbly texture.
ふにゃふにゃ
ふにゃふにゃ is similar but often used for things that are soft and lack firmness, like overcooked noodles, whereas へなへな focuses on weakness and lack of strength.

Mimetic word; the exact origin is uncertain, but it phonetically imitates a state of limpness or weakness.