Abarim Publications' online Biblical Hebrew Dictionary
The verb פתר (patar) means to interpret dreams. This verb's sole derivation is the masculine noun פתרון (pitron), meaning interpretation. Both the verb and the noun occur in the Bible only in Genesis 40 and 41, where Joseph interprets the dreams of his fellow inmates and finally the Pharaoh.
BDB Theological Dictionary reports a basic meaning of dissolve, hence solve and interpret, based on similar words in cognate languages. In post-OT texts this word became commonly used to denote explanations of or commentaries on Scriptures.
Note that the ability to interpret dreams is strongly tied to the coming of the Word in the Flesh in Jesus of Nazareth. The evangelist Matthew reports five instances of it, between Matthew 1:20 to 2:22, and in all but one of these, Jesus' father Joseph is the one doing the interpreting.
For more on dreams and interpretation of dreams, see our article on the verb חלם (halam), to dream.