WordNet (r) 3.0 (2006):

fill out
    v 1: write all the required information onto a form; "fill out
         this questionnaire, please!"; "make out a form" [syn:
         complete, fill out, fill in, make out]
    2: make bigger or better or more complete [syn: round out,
       fill out]
    3: supplement what is thought to be deficient; "He eked out his
       meager pay by giving private lessons"; "Braque eked out his
       collages with charcoal" [syn: eke out, fill out]
    4: line or stuff with soft material; "pad a bra" [syn: pad,
       fill out]
    5: make fat or plump; "We will plump out that poor starving
       child" [syn: fatten, fat, flesh out, fill out,
       plump, plump out, fatten out, fatten up]
    6: become round, plump, or shapely; "The young woman is fleshing
       out" [syn: round, flesh out, fill out]

Moby Thesaurus II by Grady Ward, 1.0:

173 Moby Thesaurus words for "fill out":
   abide by, accomplish, add to, adhere to, administer, admit,
   aggrandize, amplify, assimilate, augment, balloon, bloat, book,
   boost, bring to completion, bring to fruition, broaden, build,
   build up, bulk, calendar, carry out, carry through, carve, catalog,
   chalk, chalk up, chatter, check in, chronicle, complete,
   comprehend, comprise, cone, contain, count in, cover, crescendo,
   cut, develop, dilate, discharge, distend, docket, drag out,
   draw out, effect, effectuate, eke out, embody, embrace, encircle,
   enclose, encompass, enforce, engrave, enlarge, enroll, enscroll,
   enter, envisage, exalt, execute, expand, extend, fatten, file,
   fill, fill in, fulfill, grave, greaten, hike, hike up, hold, honor,
   impanel, implement, incise, include, incorporate, increase, index,
   inflate, inscribe, insert, jack up, jot down, jump up, lengthen,
   list, log, make, make a memorandum, make a note, make an entry,
   make good, make out, make up, mark down, matriculate, mature,
   maximize, minute, never finish, note, note down, number among,
   observe, occupy, pad, parlay, perorate, piece out,
   place upon record, poll, post, post up, promulgate, prosecute,
   protract, puff up, put down, put in force, put in writing,
   put on paper, put on tape, put through, put up, pyramid, raise,
   receive, reckon among, reckon in, reckon with, record,
   reduce to writing, refill, register, render, replenish, rotund,
   round, round out, run out, set down, snowball, speak at length,
   spin out, stretch, stretch out, string out, swell, tabulate,
   take down, take in, take into account, take into consideration,
   take up, tape, tape-record, thicken, top off, transact, tumefy, up,
   videotape, widen, write, write down, write in, write out,
   write up