WordNet (r) 3.0 (2006):

old man
    n 1: a man who is very old [syn: old man, greybeard,
         graybeard, Methuselah]
    2: a familiar term of address for a man [syn: old boy, old
       man]
    3: an informal term for your father
    4: aromatic herb of temperate Eurasia and North Africa having a
       bitter taste used in making the liqueur absinthe [syn:
       common wormwood, absinthe, old man, lad's love,
       Artemisia absinthium]
    5: (slang) boss

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "old man":
   Casanova, Don Juan, Father Time, Lothario, Methuselah, Nestor,
   Old Paar, Romeo, abba, amoroso, antediluvian, antique, back number,
   beau, benedict, boyfriend, caballero, cavalier, cavaliere servente,
   centenarian, conservative, dad, daddy, dodo, dotard, elder,
   esquire, father, fellow, flame, fogy, fossil, foster father, fud,
   fuddy-duddy, gaffer, gallant, geezer, genitor, gigolo, golden-ager,
   goodman, governor, grampa, gramps, grandfather, grandpa, grandsire,
   granny, graybeard, great-grandfather, has-been, husband, inamorato,
   lady-killer, longhair, love-maker, man, married man, matriarch,
   mid-Victorian, mossback, necker, nonagenarian, octogenarian,
   old believer, old chap, old codger, old crock, old dodo, old dog,
   old duffer, old fogy, old geezer, old gent, old gentleman,
   old liner, old party, old poop, old woman, old-timer, older,
   oldster, pa, pantaloon, pap, papa, pappy, pater, paterfamilias,
   patriarch, petter, philanderer, pop, pops, presbyter, reactionary,
   regular old fogy, relic, seducer, senior citizen, septuagenarian,
   sexagenarian, sheik, sire, square, squire, starets, stepfather,
   sugar daddy, swain, the old man, the quiet-voiced elders,
   traditionalist, venerable sir, veteran, young man