Yes, long is playable
...and is worth 8 points.
Found in the following dictionaries
Enable (Words with friends)
SOWPODS (Collins Scrabble Words)
OTCWL2014 (NASPA Word List 2014)
TWL06 (NASPA List 2006)
"Long" Definition
noun
A garment size for a tall person.
Linguistics A long syllable, vowel, or consonant.
One who acquires holdings in a security or commodity in expectation of a rise in price.
Trousers extending to the feet or ankles.
adverb
At a point of time distant from that referred to: That event took place long before we were born.
At or to a considerable distance; far: She walked long past the end of the trail.
Beyond a given boundary, limit, or goal: hit the return long.
During or for an extended period of time: The promotion was long due.
For or throughout a specified period: They talked all night long.
idiom
Long ago A time well before the present: heroes of long ago.
Long ago At a time or during a period well before the present: I read that book long ago.
Long in the tooth Growing old.
No longer Not now as formerly: He no longer smokes.
adjective
Being of relatively great duration. Used of a syllable in quantitative prosody.
Concerned with distant issues; far-reaching: took a long view of the geopolitical issues.
Extending beyond an average or standard: a long game.
Extending or landing beyond a given boundary, limit, or goal: Her first serve was long.
Extending or traveling a relatively great distance.
verb-intransitive
To have an earnest, heartfelt desire, especially for something beyond reach.
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