noun which may take the genitive case particle 'no', adverb
by nature; through and through; at heart
Describes an inherent quality or disposition that is fundamental to a person or thing. Often used with ～だ or ～の.
彼は根っから正直な人だ。
He is an honest person through and through.
根っからの
Being a city kid at heart, country life is difficult for him.
noun which may take the genitive case particle 'no', adverb
absolutely (not); (not) at all
Used with a negative verb to express complete negation. The pattern is 根っから～ない.
彼の言い訳は根っから信じられない。
I absolutely cannot believe his excuse.
あの映画は根っから面白くなかった。
That movie wasn't interesting at all.