Unlettable is valid Scrabble Word

Is unlettable a scrabble word?
Official Scrabble Players Dictionary NO
Official Tournament and Club Word List NO
Collins Scrabble Words YES
Is unlettable valid Words with Friends?
Words with Friends NO

Definitions for UNLETTABLE in dictionary:

Find what other words can be done using letters: "unlettable"
https://scrabble-word.com/finder/unlettable
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