Yes, walk 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)
"Walk" Definition
noun
A place, such as a sidewalk or promenade, on which one may walk.
A route or circuit particularly suitable for walking: one of the prettiest walks in the area.
An arrangement of trees or shrubs planted in widely spaced rows.
An enclosed area designated for the exercise or pasture of livestock.
Baseball A base on balls.
verb-transitive
Baseball To allow (a batter) to go to first base by throwing four pitches ruled as balls.
Baseball To cause (a run) to score by walking a batter. Often used with in.
To accompany in walking; escort on foot: walk the children home; walked me down the hall.
To bring to a specified condition by walking: They walked me to exhaustion.
To cause to walk or proceed at a walk: walk a horse uphill.
verb-intransitive
Baseball To go to first base after the pitcher has thrown four pitches ruled as balls.
Basketball To move illegally while holding the ball; travel.
Obsolete To be in constant motion.
Slang To be acquitted: The alleged killer walked.
Slang To go out on strike.
idiom
Off To win easily or unexpectedly.
Walk (someone) through To guide (someone) deliberately through (a process), one step at a time: She walked me through the installation of new software.
Walk away from To outdo, outrun, or defeat with little difficulty.
Walk away from To survive (an accident) with very little injury.
phrasal-verb
Walk out To go on strike.
Walk out To leave suddenly, often as a signal of disapproval.
Walk over Informal To gain an easy or uncontested victory over.
Walk over Informal To treat badly or contemptuously.
Walk through To perform (a play, for example) in a perfunctory fashion, as at a first rehearsal.