[1] : The Collaborative International Dictionary of English v.0.48

rapid \rap"id\, rapids \rap"ids\ra^p"i^dz, n. cf. f.
   rapide. see rapid, a.
   the part of a river where the current moves with great
   swiftness, but without actual waterfall or cascade; sometimes
   called whitewater; -- usually used in the plural; as, the
   lachine rapids in the st. lawrence. for boaters on the river,
   it is a place that can be hazardous, with danger of capsizing
   or crashing into large rocks.
   1913 webster +pjc

         row, brothers, row, the stream runs fast,
         the rapids are near, and the daylight's past. --moore.
   1913 webster rapid-fire
see also:
rapid whitewater 

[2] : The Collaborative International Dictionary of English v.0.48

rapid \rap"id\ ra^p"i^d, a. l. rapidus, fr. rapere to
   seize and carry off, to snatch or hurry away; perhaps akin to
   gr. 'arpa`zein: cf. f. rapide. cf. harpy, ravish.
   1913 webster
   1. very swift or quick; moving with celerity; fast; as, a
      rapid stream; a rapid flight; a rapid motion.
      1913 webster

            ascend my chariot; guide the rapid wheels. --milton.
      1913 webster

   2. advancing with haste or speed; speedy in progression; in
      quick sequence; as, rapid growth; rapid improvement; rapid
      recurrence; rapid succession.
      1913 webster

   3. quick in execution; as, a rapid penman.
      1913 webster rapid
see also:
harpy ravish 

[3] : WordNet (r) 2.0

rapid
     adj 1: done or occurring in a brief period of time; "a rapid rise
            through the ranks"
     2: characterized by speed; moving with or capable of moving
        with high speed; "a rapid movment"; "a speedy car"; "a
        speedy errand boy" syn: speedy
     n : a part of a river where the current is very fast
see also:
speedy 

[4] : Moby Thesaurus II by Grady Ward, 1.0

85 moby thesaurus words for "rapid":
   abrupt, agile, alacritous, bluff, bold, breakneck, brisk,
   ceaseless, chattering, chute, constant, continual, dashing,
   double-quick, eagle-winged, expeditious, express, fast, fleet,
   flying, galloping, hair-trigger, hasty, headlong, high-speed,
   hurried, hustling, immediate, impetuous, incessant, instant,
   instantaneous, light of heel, light-footed, lively, machine gun,
   mercurial, nimble, nimble-footed, oscillating, perennial,
   perpetual, plunging, precipitate, precipitous, prompt, pulsating,
   quick, quick as lightning, quick as thought, rapids, reckless,
   regular, repeated, riff, riffle, ripple, running, sault, sharp,
   sheer, shoot, snappy, spanking, speedy, staccato, steady, steep,
   stuttering, sudden, sustained, swift, unbroken, unceasing,
   unchanging, unintermitted, unintermittent, unintermitting,
   uninterrupted, unremitting, unstopped, unvarying, vertical,
   vibrating, winged

[5] : Virtual Entity of Relevant Acronyms (Version 1.9, June 2002)

rapid
     resource and performance interactive display system
     
     

Rapid >> R Words
Rapid, definition of term: Rapid
rapid_pag1.html

Rapid Transit >> R Words
Rapid Transit, definition of term: Rapid Transit
rapid+transit_pag1.html

Rapid Prototypi >> R Words
Rapid Prototypi, definition of term: Rapid Prototypi
rapid+prototypi_pag1.html

Rapid Growth >> R Words
Rapid Growth, definition of term: Rapid Growth
rapid+growth_pag1.html

Rapid Applicati >> R Words
Rapid Applicati, definition of term: Rapid Applicati
rapid+applicati_pag1.html