WordNet (r) 3.0 (2006):

tauten
    v 1: become taut or tauter; "Your muscles will firm when you
         exercise regularly"; "the rope tautened" [syn: tauten,
         firm]
    2: make taut or tauter; "tauten a rope" [syn: tauten, firm]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "tauten":
   continue, crank, crank in, drag out, draw, draw in, draw out,
   draw taut, elongate, extend, lengthen, lengthen out, let out,
   produce, prolong, prolongate, protract, pull, pull in, reel,
   reel in, spin out, strain, stretch, stretch out, string out,
   tackle, tense, tighten, trim, winch, wind in, windlass