There is only one Hamutal in the Bible, and she is the mother of kings Jehoahaz and Zedekiah of Judah (2 Kings 23:31 & 24:18). She is a daughter of Jeremiah of Libnah (who is not the famous prophet) and the wife of king Josiah (2 Kings 23:30).
The first part of the name may be the word (ham), meaning hot (see the name Ham). But that would give this name a meaning of Hot Dew, and that's most likely incorrect. More likely is a kinship with the similar word (ham) meaning father in law. The whole name thus means My Father In Law Is The Dew. Whatever poetic or other image the Hebrews had with this name is unclear, but that there must have been something is strongly argued by the existence of the similar name Abital, meaning My Father Is The Dew.
For a meaning of the name Hamutal, NOBS Study Bible Name List reads a timid (and ultimately incorrect) Kinsman Of Dew. Jones' Dictionary of Old Testament Proper Names reads an evenly deviated Akin To The Dew. BDB Theological Dictionary states "meaning dubious; perhaps, if Kethibh is right, My Husband's Father Is The Dew.