WordNet (r) 3.0 (2006):

let out
    v 1: express audibly; utter sounds (not necessarily words); "She
         let out a big heavy sigh"; "He uttered strange sounds that
         nobody could understand" [syn: utter, emit, let out,
         let loose]
    2: make known to the public information that was previously
       known only to a few people or that was meant to be kept a
       secret; "The auction house would not disclose the price at
       which the van Gogh had sold"; "The actress won't reveal how
       old she is"; "bring out the truth"; "he broke the news to
       her"; "unwrap the evidence in the murder case" [syn:
       unwrap, disclose, let on, bring out, reveal,
       discover, expose, divulge, break, give away, let
       out]
    3: bring out of a specific state [syn: bring out, let out]
    4: make (clothes) larger; "Let out that dress--I gained a lot of
       weight" [syn: let out, widen] [ant: take in]

Moby Thesaurus II by Grady Ward, 1.0:

227 Moby Thesaurus words for "let out":
   air, articulate, ax, bare, betray, bleed, blow, boot, boot out,
   bounce, break, break it to, break the news, break the seal,
   breathe, breathe out, bring to light, broach, bump, bust, can,
   cashier, cast loose, charter, chime, chorus, come out with,
   communicate, confide, confide to, continue, convey, decant,
   defrock, degrade, deliver, demobilize, demote, deplume, depose,
   deprive, develop, disbar, discharge, disclose, discover, disemploy,
   dismask, dismiss, displace, displume, divulgate, divulge, draft,
   draft off, drag out, drain, draw, draw from, draw off, draw out,
   draw the veil, drop, drum out, elongate, emit, empty, enunciate,
   evacuate, evulgate, exhale, exhaust, expel, expire, expose,
   express, extend, farm, farm out, fire, fling off, formulate, fume,
   furlough, give, give away, give expression, give off, give out,
   give out with, give the ax, give the gate, give tongue,
   give utterance, give vent to, give voice, go bail for,
   grant bail to, hire, hire out, impart, job, kick, kick upstairs,
   lay bare, lay off, lay open, lease, lease out, lease-back,
   lease-lend, lend-lease, lengthen, lengthen out, let, let blood,
   let daylight in, let get around, let go, let go free, let in on,
   let loose, let off, lip, make known, make redundant, manifest,
   milk, mouth, open, open the floodgates, open the sluices, open up,
   out with, parole, pension off, phlebotomize, phonate, phrase,
   pipette, pour forth, present, produce, prolong, prolongate,
   pronounce, protract, publish, puff, pull, pump, pump out,
   put forth, put in words, put on parole, raise, raise the curtain,
   read out of, reek, release, remove, rent, rent out, replace,
   retire, reveal, sack, say, separate forcibly, set forth, show,
   show up, siphon off, smoke, sound, spill, spin out, steam, strain,
   stretch, stretch out, string out, strip, strip bare, sublease,
   sublet, suck, suck out, superannuate, surplus, suspend, tap,
   tauten, tell, tense, terminate, throw off, tighten, turn off,
   turn out, uncloak, uncover, underlet, undrape, unfold, unfrock,
   unfurl, unhand, unkennel, unmask, unpack, unroll, unscreen,
   unsheathe, unshroud, unveil, unwrap, utter, vapor, venesect, vent,
   ventilate, verbalize, vocalize, voice, whisper, word