na-adjective
tough; tenacious; stubborn; determined
Describes a person or attitude that is resilient, unyielding, or shrewdly persistent. Often carries a nuance of being hard to beat or not easily swayed.
彼はしたたかな交渉相手だ。
He is a tough negotiator.
あの選手はしたたか
That player is tenacious and won't lose easily.
adverb
severely; heavily; hard; a great deal
Adverbial use meaning to do something intensely, heavily, or to a great degree. Often used with verbs like 飲む (drink) or やる (do).
昨夜はしたたか飲んだ。
I drank heavily last night.
彼はしたたかやられたようだ。
He seems to have been beaten badly.
The origin is uncertain. The word is native Japanese, and the kanji 強 and 健 are applied for their meanings, but the kana spelling is standard.