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 .
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 .
idiom
All along From the beginning; throughout: saw through the disguise all along.
All but Nearly; almost: all but crying with relief.
All in all Everything being taken into account: All in all, the criticism seemed fair.
All of Informal Not more than: a conversation that took all of five minutes.
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.
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