What It Scores
HM is a valid word in the tournament list this site uses. Tile values only, before any premium square: 7 in Scrabble, 7 in Words With Friends, 7 in Wordfeud. The letters break down as H4 M3.
Longer Words Containing HM
HM appears inside each of these, which is what makes it worth knowing as a hook.
Next: the Word Unscrambler for any letters at all, and the two and three letter lists. Full entry and definition at Merriam-Webster.