Wiktionary
vb. had better.
WordNet
v. act in one's own or everybody's best interest; "You will do well to arrive on time tomorrow!" [syn: do well]
Usage examples of "had best".
Whatever it was, it was clear she had best not put it off too long.
Burton reflected that if the Ethicals had intended to record all human tongues, They had best hurry.
One of us had best stay here with the boat, Terence said, looking severely at Cyril.
If they were to breed they had best get on with it, and better to start with the older female.
When Hackworth had performed this stunt as a youth, he had discovered that the farther it got from its appointed place the hotter it became, all the while politely informing him, in clipped military diction, that he had best release it or fall victim to vaguely adumbrated consequences.