The Collaborative International Dictionary of English v.0.48:

Nap \Nap\ (n[a^]p), v. i. [imp. & p. p. Napped (n[a^]pt); p.
   pr. & vb. n. Napping (n[a^]p"p[i^]ng).] [OE. nappen, AS.
   hn[ae]ppian to take a nap, to slumber; cf. AS. hnipian to
   bend one's self, Icel. hnipna, hn[imac]pa, to droop.]
   1. To have a short sleep; to be drowsy; to doze. --Chaucer.
      [1913 Webster]

   2. To be in a careless, secure state; to be unprepared; as,
      to be caught napping. --Wyclif.
      [1913 Webster +PJC]

            I took thee napping, unprepared.      --Hudibras.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Napping \Nap"ping\, n.
   1. The act or process of raising a nap, as on cloth.
      [1913 Webster]

   2. (Hat Making) A sheet of partially felted fur before it is
      united to the hat body. --Knight.
      [1913 Webster]

   3. The act or process of having a short sleep; as, napping is
      a common occupation for cats.
      [PJC]

WordNet (r) 3.0 (2006):

napping
    adj 1: not prepared or vigilant; "the blow caught him napping";
           "caught in an off-guard moment"; "found him off his
           guard" [syn: napping, off-guard(a), off guard(p),
           off one's guard(p), off his guard, off her guard,
           off your guard]

Moby Thesaurus II by Grady Ward, 1.0:

117 Moby Thesaurus words for "napping":
   a stranger to, absent, absentminded, absorbed, abstracted,
   anesthetized, asleep, bemused, blind to, castle-building,
   cataleptic, caught napping, comatose, daydreaming, daydreamy,
   dead to, deaf to, doped, dozy, dreaming, dreamy, drowsing, drowsy,
   drugged, drugged with sleep, ecstatic, elsewhere, engrossed,
   faraway, goofing off, half asleep, half-awake, heavy,
   heavy with sleep, heavy-eyed, impercipient, in a reverie,
   in a stupor, in ignorance of, in the clouds, incautious,
   incognizant, insensible, insensible to, languid, lethargic, lost,
   lost in thought, meditative, mindless, mooning, moonraking,
   museful, musing, narcoleptic, narcose, narcotized, narcous,
   nodding, nonconceiving, not with it, oblivious, off-guard,
   oscitant, out of it, pensive, pipe-dreaming, preoccupied, rapt,
   sedated, sleep-drowned, sleep-drunk, sleep-filled, sleep-swollen,
   sleepful, sleeping, sleepy, slumberous, slumbery, snoozy,
   somewhere else, somnolent, soporific, stargazing, stretchy,
   stuporose, stuporous, taken up, transported, unalert, unaware,
   unaware of, uncautious, unconscious, unconscious of, unguarded,
   unhearing, uninsightful, unknowing, unmindful, unmindful of,
   unperceiving, unprehensive, unprepared, unready, unrealizing,
   unseeing, unsuspecting, unvigilant, unwary, unwatchful, unwitting,
   witless, woolgathering, wrapped in thought, yawning, yawny