Source : Webster's Revised Unabridged Dictionary (1913)

Sprain \Sprain\, v. t. [imp. & p. p. {Sprained}; p. pr. & vb. n.
   {Spraining}.] [OF. espreindreto press, to force out, F.
   ['e]preindre, fr. L. exprimere. See {Express}, v. t., and cf.
   {Spraints}.]
   To weaken, as a joint, ligament, or muscle, by sudden and
   excessive exertion, as by wrenching; to overstrain, or
   stretch injuriously, but without luxation; as, to sprain
   one's ankle.