The Collaborative International Dictionary of English v.0.48:

Rocket \Rock"et\, n. [F. roquette (cf. Sp. ruqueta, It
   ruchetta), fr. L. eruca.] (Bot.)
   (a) A cruciferous plant (Eruca sativa) sometimes eaten in
       Europe as a salad.
   (b) Damewort.
   (c) Rocket larkspur. See below.
       [1913 Webster]

   Dyer's Rocket. (Bot.) See Dyer's broom, under Broom.

   Rocket larkspur (Bot.), an annual plant with showy flowers
      in long racemes (Delphinium Ajacis).

   Sea rocket (Bot.), either of two fleshy cruciferous plants
      (Cakile maritima and Cakile Americana) found on the
      seashore of Europe and America.

   Yellow rocket (Bot.), a common cruciferous weed with yellow
      flowers (Barbarea vulgaris).
      [1913 Webster]

WordNet (r) 3.0 (2006):

rocket larkspur
    n 1: commonly cultivated larkspur of southern Europe having
         unbranched spikelike racemes of blue or sometimes purplish
         or pinkish flowers; sometime placed in genus Delphinium
         [syn: rocket larkspur, Consolida ambigua, Delphinium
         ajacis]