Yes. MUMM is a valid word.
MUMM is in the NASPA Word List 2023 (NWL2023), the North American list that Tileside uses for challenges and the one used in club and tournament play.
Settle the next one at the table: score your game free in Tileside →
MUMM scores 7 points
Before any bonus squares: M 3 + U 1 + M 3 + blank M 0 = 7. On a double-word square that's 14, on a triple-word 21, and every letter bonus under one of these tiles is applied first.
MUMM needs a blank: the bag has two M tiles.
Hooks: one tile makes a new word
Check words at the table, free
Tileside keeps score, checks words like this one during a challenge, tracks the tiles left in the bag and times turns. It runs in your phone's browser with no account and works offline.
Tileside checks words against the North American list, the NASPA Word List 2023. Your group's chosen dictionary always wins.
Word list: NASPA Word List 2023, used under license. NASPA Word List 2023 Edition © NASPA 2023. The copy included in this app is licensed for personal use. You may not use it for any commercial purposes.