The Collaborative International Dictionary of English v.0.48:

Promptness \Prompt"ness\, n.
   [1913 Webster]
   1. Promptitude; readiness; quickness of decision or action.
      [1913 Webster]

   2. Cheerful willingness; alacrity.
      [1913 Webster]

WordNet (r) 3.0 (2006):

promptness
    n 1: the characteristic of doing things without delay [syn:
         promptness, promptitude]
    2: the quality or habit of adhering to an appointed time [syn:
       punctuality, promptness] [ant: tardiness]

Moby Thesaurus II by Grady Ward, 1.0:

138 Moby Thesaurus words for "promptness":
   OK, abruptness, acceptance, accord, acquiescence, acuity,
   acuteness, affirmation, affirmative, affirmative voice, agility,
   agreeability, agreeableness, agreement, air speed, alacrity,
   alertness, amenability, animation, anxiety, anxiousness, appetite,
   approbation, approval, ardor, assent, attention, attentiveness,
   avidity, avidness, aye, blessing, breathless impatience,
   brightness, briskness, celerity, cheerful consent,
   cheerful readiness, compliance, connivance, consent,
   cooperativeness, decisiveness, dispatch, docility, eagerness, elan,
   endorsement, enthusiasm, expedition, expeditiousness, fastness,
   favorable disposition, favorableness, feverishness, flight, flit,
   flurry, forwardness, furiousness, gameness, goodwill, ground speed,
   gust, gusto, haste, hastiness, hurriedness, hurry, immediacy,
   immediateness, impatience, impetuosity, impetuousness,
   impulsiveness, instantaneousness, keen desire, keenness, knots,
   life, lightning speed, liveliness, miles per hour, nimbleness,
   okay, permission, pliability, pliancy, precipitance, precipitancy,
   precipitation, precipitousness, promptitude, punctuality,
   punctualness, quickness, rapidity, rashness, ratification,
   readiness, receptive mood, receptiveness, receptivity,
   responsiveness, right mood, round pace, rpm, rush, sanction,
   sharpness, sleeplessness, smartness, snappiness, speed, speediness,
   spirit, spryness, submission, suddenness, summariness, swift rate,
   swiftness, tractability, ungrudgingness, unloathness, unreluctance,
   velocity, verve, vitality, vivacity, wakefulness, willing ear,
   willing heart, willingness, zeal, zealousness, zest, zestfulness