phải

must(verb)

used with another verb to express need

We must go to the shops to get milk.

cần

must(verb)

used, usually with another verb, to suggest a probability

They must be finding it very difficult to live in such a small house.

chắc hẳn

must(noun)

something necessary, essential, or not to be missed

This new tent is a must for the serious camper.

cần thiết

must(verb)

used, usually with another verb, to express duty, an order, rule etc

You must come home before midnight; All competitors must be under 15 years of age.