汰 (tài) is a bound form (b.f.) that does not appear alone in modern Chinese; it always combines with another morpheme to form a compound or chengyu. The core meaning is 'to eliminate through competition or selection', most often seen in 淘汰 (táotài, 'to weed out, to eliminate') and the idiom 优胜劣汰 (yōushèng liètài, 'survival of the fittest'). Whenever you encounter 汰, think of it as the second element of 淘汰 or the last character of a chengyu — never use it by itself.