The Collaborative International Dictionary of English v.0.48:

Hold \Hold\, v. i.
   In general, to keep one's self in a given position or
   condition; to remain fixed. Hence:
   [1913 Webster]

   1. Not to move; to halt; to stop; -- mostly in the
      imperative.
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            And damned be him that first cries, "Hold, enough!"
                                                  --Shak.
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   2. Not to give way; not to part or become separated; to
      remain unbroken or unsubdued.
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            Our force by land hath nobly held.    --Shak.
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   3. Not to fail or be found wanting; to continue; to last; to
      endure a test or trial; to abide; to persist.
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            While our obedience holds.            --Milton.
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            The rule holds in land as all other commodities.
                                                  --Locke.
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   4. Not to fall away, desert, or prove recreant; to remain
      attached; to cleave; -- often with with, to, or for.
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            He will hold to the one and despise the other.
                                                  --Matt. vi. 24
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   5. To restrain one's self; to refrain.
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            His dauntless heart would fain have held
            From weeping, but his eyes rebelled.  --Dryden.
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   6. To derive right or title; -- generally with of.
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            My crown is absolute, and holds of none. --Dryden.
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            His imagination holds immediately from nature.
                                                  --Hazlitt.
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   Hold on! Hold up! wait; stop; forbear. [Collog] -- To
   hold forth, to speak in public; to harangue; to preach.
      --L'Estrange.

   To hold in, to restrain one's self; as, he wanted to laugh
      and could hardly hold in.

   To hold off, to keep at a distance.

   To hold on, to keep fast hold; to continue; to go on. "The
      trade held on for many years," --Swift.

   To hold out, to last; to endure; to continue; to maintain
      one's self; not to yield or give way.

   To hold over, to remain in office, possession, etc., beyond
      a certain date.

   To hold to or To hold with, to take sides with, as a
      person or opinion.

   To hold together, to be joined; not to separate; to remain
      in union. --Dryden. --Locke.

   To hold up.
      (a) To support one's self; to remain unbent or unbroken;
          as, to hold up under misfortunes.
      (b) To cease raining; to cease to stop; as, it holds up.
          --Hudibras.
      (c) To keep up; not to fall behind; not to lose ground.
          --Collier.
          [1913 Webster]

WordNet (r) 3.0 (2006):

hold on
    v 1: hold firmly [syn: grasp, hold on]
    2: stop and wait, as if awaiting further instructions or
       developments; "Hold on a moment!" [syn: hold on, stop]
    3: be persistent, refuse to stop; "he persisted to call me every
       night"; "The child persisted and kept asking questions" [syn:
       persevere, persist, hang in, hang on, hold on]
    4: hold the phone line open; "Please hang on while I get your
       folder" [syn: hang on, hold the line, hold on]
    5: retain possession of; "Can I keep my old stuffed animals?";
       "She kept her maiden name after she married" [syn: keep,
       hold on] [ant: lose]

Moby Thesaurus II by Grady Ward, 1.0:

178 Moby Thesaurus words for "hold on":
   abide, adhere, adhere to, agglomerate, aim, aim at, await,
   be caught short, be short, bear up, belong, bend, bide,
   bide the issue, bite, bucket, bucketshop, bunch, carry on,
   cease not, clasp, cleave, cleave to, clench, clinch, cling,
   cling to, clip, clot, cluster, clutch, coagulate, cohere,
   come up fighting, congeal, conglomerate, continue, continue to be,
   dally, dawdle, defeat time, defy time, delay, deposit margin,
   determine, dillydally, direct, directionize, drag on, dwell,
   embrace, endure, exist, extend, fix, fix on, freeze to, go along,
   go long, go on, grapple, grasp, grip, gripe, grow together,
   hang about, hang around, hang in, hang in there, hang on,
   hang on to, hang together, hang tough, hold, hold everything,
   hold fast, hold on to, hold out, hold steady, hold tight,
   hold together, hold up, hold your horses, hug, jog on, keep,
   keep going, keep hold of, keep on, last, last long, last out,
   level at, linger, live, live on, live through, live through it,
   live with it, loiter, maintain, make a killing, make a scoop,
   margin up, mark time, mass, miss the market, never cease,
   never let go, never say die, nip, not give up, operate,
   overstay the market, perdure, perennate, persist, play the market,
   plunge, point, point at, point to, present, prevail, pyramid,
   remain, run, run on, scalp, scoop the market, set, sight on,
   sit tight, sit up, slog on, solidify, speculate, stag,
   stag the market, stagger on, stand, stand up, stay, stay it out,
   stay on, stay put, stay the distance, stay up, stay with it, stick,
   stick around, stick it, stick it out, stick out, stick to,
   stick to it, stick together, stick with it, subsist, survive,
   sustain, take a flier, take hold of, take time, tarry, tide over,
   tough it out, trade on margin, train, train upon, turn, turn upon,
   venture, wait, wait a minute, wait and see, wear, wear well