In all languages, a relative pronoun is a DMW; i.e. it introduces a dependent clause.
English:
Who, whom, which, that, what and whose are the relative pronouns. (more)
A relative pronoun is one of the two kinds of DMWs. When the DMW is a relative pronoun, it indicates that the dependent clause is most likely adjectival.
Greek:
In Greek, the relative pronoun is declined for number, case, and gender. It is distinguished from the article by reason of the fact that it always has a rough breathing mark which the article usually does not. Study chapter 14 in BBG.
Hebrew:
The word אֲשֶׁר is the relative pronoun in Hebrew. Study this or this video.
