对头 has two different tones and meanings: duìtóu (2nd tone on 头) means 'correct/right,' while duìtou (neutral tone on 头) means 'rival/adversary.' The written form is the same.
usage
不对头 (bù duìtóu) is a very common colloquial expression meaning 'something is off' or 'something doesn't seem right.' It's used to express suspicion or unease.
