Yes. POSSET is a valid word.
POSSET 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.
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POSSET scores 8 points
Before any bonus squares: P 3 + O 1 + S 1 + S 1 + E 1 + T 1 = 8. On a double-word square that's 16, on a triple-word 24, and every letter bonus under one of these tiles is applied first.
Hooks: one tile makes a new word
After POSSET (1):
Place that one tile so it also forms a word in the other direction and both words score.
Same letters, other words
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.