Definition: to criticize someone and make him or her appear foolish or unimportant.
(This phrasal verb has more than one meaning)
E.g.1: She put him down by reminding him of his performance in the previous test.
E.g.2: He tries to make himself seem more knowledgeable by putting down the other members of the group.
This phrasal verb can be separated. (E.g. 1)