WordNet (r) 3.0 (2006):

hang on
    v 1: fix to; attach; "append a charm to the necklace" [syn:
         append, tag on, tack on, tack, hang on]
    2: 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]
    3: hold the phone line open; "Please hang on while I get your
       folder" [syn: hang on, hold the line, hold on]

Moby Thesaurus II by Grady Ward, 1.0:

155 Moby Thesaurus words for "hang on":
   account for, accredit with, accrete to, accrue from, acknowledge,
   adhere, adhere to, agglomerate, all depend, apply to, arise from,
   ascribe to, assign to, attach to, attribute to, be based on,
   be contingent on, be dependent on, be due to, be predicated on,
   be spared, bear up, bite, blame, blame for, blame on,
   bring home to, bud from, bunch, carry on, charge on, charge to,
   cheat death, clasp, cleave, cleave to, clench, clinch, cling,
   cling to, clip, clot, cluster, clutch, coagulate, cohere,
   come from, come out of, come up fighting, confess, congeal,
   conglomerate, connect with, credit with, depend, depend on,
   derive from, descend from, emanate from, embrace, emerge from,
   endure, ensue from, fasten upon, father upon, fix on, fix upon,
   flow from, follow from, freeze to, germinate from, go on, grapple,
   grasp, grip, gripe, grow from, grow out of, grow together, hang,
   hang in, hang in suspense, hang in there, hang on to,
   hang together, hang tough, hinge, hinge on, hold, hold fast,
   hold on, hold on to, hold out, hold tight, hold together, hold up,
   hug, impute to, issue from, keep alive, keep hold of, last, lay to,
   lie on, lie with, live through it, live with it, mass,
   never let go, never say die, nip, not give up, originate in, pend,
   persist, pin on, pinpoint, place upon, point to, proceed from,
   refer to, rest, rest on, rest with, revolve on, saddle on,
   saddle with, set, set down to, settle upon, solidify, spring from,
   sprout from, stand on, stand up, stay, stay it out, stay put,
   stay the distance, stay with it, stem from, stick, stick it,
   stick it out, stick out, stick to, stick to it, stick together,
   stick with it, support life, survive, take hold of, tough it out,
   turn on, turn upon