対 (Kanji for against)

JERK: Usually, it means "against", and is pronounced TAI, but very occasionally it means "pair" - the OPPOSITE being against!

Also, when it's used to mean "pair", it's pronounced つい, but probably you don't need that one.

Onyomi

TAI

In May, it is fashionable to glue a neckTIE against your beret.

絶対(ぜったい) に	absolutely, without fail ★★★★☆ 絶 (extinct) + 対 (against) = 絶対 (absolutely, without fail)
反対(はんたい) する	against it!!!!!!!!!! ★★★★☆ 反 (anti) + 対 (against) = 反対 (against it!!!!!!!!!!) to be against something
対策(たいさく)	counter-plan / counter-measure ★★★☆☆ 対 (against) + 策 (take measures) = 対策 (counter-plan / counter-measure)
反対派(はんたいは)	the opposing faction ☆☆☆☆☆ 反対 (against it!!!!!!!!!!) + 派 (faction/bling) = 反対派 (the opposing faction)