From WordNet (r) 3.0 (2006) [wn]:
lobster
n 1: flesh of a lobster
2: any of several edible marine crustaceans of the families
Homaridae and Nephropsidae and Palinuridae
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Lobster \Lob"ster\, n. [AS. loppestre, lopystre prob., corrupted
fr. L. locusta a marine shellfish, a kind of lobster, a
locust. Cf. Locust.] (Zool.)
1. Any large macrurous crustacean used as food, esp. those of
the genus Homarus; as the American lobster ({Homarus
Americanus}), and the European lobster ({Homarus
vulgaris}). The Norwegian lobster (Nephrops Norvegicus)
is similar in form. All these have a pair of large unequal
claws. The spiny lobsters of more southern waters,
belonging to Palinurus, Panulirus, and allied genera,
have no large claws. The fresh-water crayfishes are
sometimes called lobsters.
[1913 Webster]
2. As a term of opprobrium or contempt: A gullible, awkward,
bungling, or undesirable person. [Slang]
[Webster 1913 Suppl.]
Lobster caterpillar (Zool.), the caterpillar of a European
bombycid moth (Stauropus fagi); -- so called from its
form.
Lobster louse (Zool.), a copepod crustacean ({Nicotho["e]
astaci}) parasitic on the gills of the European lobster.
[1913 Webster]