Yes, back is playable
...and is worth 14 points.
Found in the following dictionaries
Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)
"Back" Definition
noun
A part that supports or strengthens from the rear: the back of a couch.
A shallow vat or tub used chiefly by brewers.
Sports A player who takes a position behind the front line of other players in certain games, such as football and soccer.
Sports This playing position.
The analogous dorsal region in other animals.
adverb
At, to, or toward the rear or back; backward.
In check or under restraint: Barriers held the crowd back.
In reserve or concealment.
In, to, or toward a former condition.
idiom
Back and fill Nautical To maneuver a vessel in a narrow channel by adjusting the sails so as to let the wind in and out of them in alteration.
Back to back Consecutively and without interruption: presented three speeches back to back.
phrasal-verb
Back away To withdraw from a position; retreat.
Back down To withdraw from a position, opinion, or commitment.
Back off To retreat or draw away.
Back out To fail to keep a commitment or promise.
Back out To withdraw from something before completion.
adjective
Being in a backward direction.
Being owed or due from an earlier time; in arrears: back pay.
Distant from a center of activity; remote.
Linguistics Pronounced with the back of the tongue, as oo in cool. Used of vowels.
Located or placed in the rear: Deliveries should be made at the back entrance.
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