Yes, all is playable
...and is worth 5 points.
Found in the following dictionaries
Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)
"All" Definition
noun
The whole of one's possessions, resources, or energy .
adjective
Any whatsoever: beyond all doubt.
Being or representing the entire or total number, amount, or quantity: All the windows are open. Deal all the cards. See Synonyms at whole.
Being the utmost possible of: argued the case in all seriousness.
Constituting, being, or representing the total extent or the whole: all Christendom.
Every: got into all manner of trouble.
adverb
Each; apiece: a score of five all.
So much: I am all the better for that experience.
Wholly; completely: a room painted all white; directions that were all wrong.
Selected as the best (as at a sport) within an area or organization .
pronoun
Everyone; everything: justice for all.
The entire or total number, amount, or quantity; totality: All of us are sick. All that I have is yours.
pronoun, singular or plural in construction
The whole number, quantity, or amount .
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