The Collaborative International Dictionary of English v.0.48:

Sea holly \Sea" hol"ly\ (Bot.)
   An evergeen seashore plant (Eryngium maritimum). See
   Eryngium.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Holly \Hol"ly\ (h[o^]l"l[y^]), n. [OE holi, holin, AS. holen,
   holegn; akin to D. & G. hulst, OHG. huls hulis, W. celyn,
   Armor. kelen, Gael. cuilionn, Ir. cuileann. Cf. 1st Holm,
   Hulver.]
   1. (Bot.) A tree or shrub of the genus Ilex. The European
      species (Ilex Aquifolium) is best known, having glossy
      green leaves, with a spiny, waved edge, and bearing
      berries that turn red or yellow about Michaelmas.
      [1913 Webster]

   Note: The holly is much used to adorn churches and houses, at
         Christmas time, and hence is associated with scenes of
         good will and rejoicing. It is an evergreen tree, and
         has a finegrained, heavy, white wood. Its bark is used
         as a febrifuge, and the berries are violently purgative
         and emetic. The American holly is the Ilex opaca, and
         is found along the coast of the United States, from
         Maine southward. --Gray.
         [1913 Webster]

   2. (Bot.) The holm oak. See 1st Holm.
      [1913 Webster]

   Holly-leaved oak (Bot.), the black scrub oak. See Scrub
      oak.

   Holly rose (Bot.), a West Indian shrub, with showy, yellow
      flowers (Turnera ulmifolia).

   Sea holly (Bot.), a species of Eryngium. See Eryngium.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sea holly
    n 1: European evergreen eryngo with twisted spiny leaves
         naturalized on United States east coast; roots formerly
         used as an aphrodisiac [syn: sea holly, sea holm, sea
         eryngium, Eryngium maritimum]
    2: widely cultivated southern European acanthus with whitish
       purple-veined flowers [syn: bear's breech, bear's
       breeches, sea holly, Acanthus mollis]