The Collaborative International Dictionary of English v.0.48:

Sniffle \Snif"fle\, v. i. [Freq. of sniff. See Snivel.]
   To snuffle, as one does with a catarrh. [Prov. Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

sniffle
    n 1: the act of breathing heavily through the nose (as when the
         nose is congested) [syn: snuffle, sniffle, snivel]
    v 1: cry or whine with snuffling; "Stop snivelling--you got
         yourself into this mess!" [syn: snivel, sniffle,
         blubber, blub, snuffle]
    2: inhale audibly through the nose; "the sick student was
       sniffling in the back row" [syn: sniff, sniffle]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "sniffle":
   Aqua-Lung, artificial respiration, aspirate, aspiration,
   assibilate, assibilation, asthmatic wheeze, blow, breath,
   breath of air, breathe, breathe hard, breathe in, breathe out,
   breathing, broken wind, buzz, cough, draw in, effervesce,
   effervescence, effervescing, exhalation, exhale, exhaust, expel,
   expiration, expire, exsufflation, fizz, fizzle, fizzling,
   frication, frictional rustling, gasp, gulp, hack, hiccup, hiss,
   hissing, huff, hush, hushing, inhalation, inhalator, inhale,
   inhalement, inspiration, inspire, insufflation, iron lung, lisp,
   mouth-to-mouth resuscitation, oxygen mask, oxygen tent, pant, puff,
   respiration, respire, rhonchus, scuba, shush, shushing, sibilance,
   sibilate, sibilation, siffle, sigh, sigmatism, siss, sissing, sizz,
   sizzle, sizzling, slurp, sneeze, sneezing, sniff, snore, snoring,
   snort, snuff, snuff in, snuffle, spit, splutter, sputter, squash,
   squelch, squish, sternutation, stertor, suck, suck in, sucking,
   suckle, suction, suspiration, swish, wheeze, whish, whistle,
   whistling, white noise, whiz, whoosh, wind, zip