The Collaborative International Dictionary of English v.0.48:

Kat \Kat\ (k[aum]t), n. (Bot.)
   An Arabian shrub (Catha edulis) the leaves of which are
   used as tea by the Arabs.
   [1913 Webster]

WordNet (r) 3.0 (2006):

kat
    n 1: the leaves of the shrub Catha edulis which are chewed like
         tobacco or used to make tea; has the effect of a euphoric
         stimulant; "in Yemen kat is used daily by 85% of adults"
         [syn: kat, khat, qat, quat, cat, Arabian tea,
         African tea]