プログレッシブ和英中辞典(第4版)の解説
そこぢから【底力】
potential [latent] energy; underlying strength
彼の真の底力を見せるチャンスだった
It was a (good) chance to show 「his real ability [what he could do/his true potential].
底力のある声
((have)) a deep voice
底力のある人
an energetic person／a person who has hidden power within him [her]／a person of real ability
あの男は小才が利くが底力はない
He's (superficially) clever but underneath he lacks what it takes.