WordNet (r) 3.0 (2006):

miles per hour
    n 1: the ratio of the distance traveled (in miles) to the time
         spent traveling (in hours) [syn: miles per hour, mph]
    2: a speedometer reading for the momentary rate of travel [syn:
       miles per hour, mph]

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "miles per hour":
   air speed, celerity, dispatch, expedition, fastness, flight, flit,
   flurry, ground speed, haste, hurry, instantaneousness, knots,
   lightning speed, precipitation, promptitude, promptness, quickness,
   rapidity, round pace, rpm, rush, snappiness, speed, speediness,
   swift rate, swiftness, velocity