noun, noun or participle which takes 'suru'
limpness; being limp
Describes a state of lacking firmness or stiffness; often used for objects that should be rigid but are not.
この麺は茹ですぎてふにゃふにゃだ。
These noodles are overcooked and limp.
Describes something that is soft and lacking firmness, often with a negative connotation of being too soft or weak.
ふにゃふにゃの枕は首が痛くなる。
A soft, limp pillow makes my neck hurt.
運動不足でお腹がふにゃふにゃになってきた。
My belly has gotten flabby from lack of exercise.
na-adjective, noun which may take the genitive case particle 'no'
mumbling; talking with food in one's mouth
Sometimes used instead of むにゃむにゃ to describe indistinct speech, especially when the mouth is full or the speaker is half-asleep.
口に物を入れたままふにゃふにゃ言わないで。
Don't mumble with food in your mouth.