Yes, double is playable
...and is worth 12 points.
Found in the following dictionaries
Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)
"Double" Definition
noun
A sharp turn in a direction of movement; a reversal.
A sharp, often devious change in position or argument; a shift.
An actor who takes the place of another actor in scenes requiring special skills or preparations: a stunt double; a body double.
Baseball See two-base hit.
adjective
Accommodating or designed for two: a double bed; a double room.
Botany Having many more than the usual number of petals, usually in a crowded or an overlapping arrangement: a double chrysanthemum.
Characterized by duplicity; deceitful: speak with a double tongue.
Composed of two like parts: double doors.
Composed of two unlike parts; dual: a double meaning; a double role for an actor.
verb-transitive
Baseball To advance or score (a runner) by hitting a two-base hit.
Baseball To cause the scoring of (a run) by hitting a two-base hit.
Baseball To put out (a runner) as the second part of a double play.
Music To duplicate (another part or voice) an octave higher or lower or in unison.
Nautical To sail around: double a cape.
verb-intransitive
Baseball To hit a two-base hit.
Games To announce a double in bridge.
To be increased twofold: The debt soon doubled.
To serve in an additional capacity: a frying pan that doubles as a pie tin; a conductor who doubles as a pianist.
phrasal-verb
Double up To bend suddenly, as in pain or laughter.
Double up To share accommodations meant for one person.
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