noun, plural (especially collectively) lobster (especially referring to two or more kinds or species) lobsters.
any of various large, edible, marine, usually dull-green, stalk-eyed decapod crustaceans of the family Homaridae, especially of the genus Homarus, having large, asymmetrical pincers on the first pair of legs, one used for crushing and the other for cutting and tearing: the shell turns bright red when cooked.
any of various similar crustaceans, as certain crayfishes.
the edible meat of these animals.

before 1000; Middle English lopster, Old English loppestre literally, spidery creature (loppe spider (see lob1) + -stre -ster); cf. lop1

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World English Dictionary
lobster (ˈlɒbstə)
n , pl -sters, -ster
1.  any of several large marine decapod crustaceans of the genus Homarus, esp H. vulgaris, occurring on rocky shores and having the first pair of limbs modified as large pincers
2.  any of several similar crustaceans, esp the spiny lobster
3.  the flesh of any of these crustaceans, eaten as a delicacy
[Old English loppestre, from loppe spider]

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

O.E. loppestre, corruption of L. locusta "lobster, locust," by influence of O.E. loppe "spider," a variant of lobbe. Trilobite fossils in Worcestershire limestone quarries were known colloquially as locusts, which seems to be the generic word for "unidentified arthropod," as apple is for "foreign fruit."
But OED says the L. word originally meant "lobster or some similar crustacean, the application to the locust being suggested by the resemblance in shape." Locusta in sense "lobster" also borrowed in Fr. (langouste), Old Cornish (legast). The ending of O.E. loppestre is the fem. agent noun suffix (cf. Baxter, Webster; see -ster), which approximated the L. sound. Slang for "a British soldier" since 1643, originally in reference to the jointed armor of the Roundhead cuirassiers, later (1660) to the red coat.
"Sir William Waller having received from London [in June 1643] a fresh regiment of five hundred horse, under the command of sir Arthur Haslerigge, which were so prodigiously armed that they were called by the other side the regiment of lobsters, because of their bright iron shells with which they were covered, being perfect curasseers." [Clarendon, "History of the Rebellion," 1647]
Online Etymology Dictionary, © 2010 Douglas Harper
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Example sentences
You'll get to hear about their private jet, the special lobster and steak
  victory meals and other perks.
About three feet from me was a lobster on display, on a bed of ice, too groggy
  to escape.
There's no better way to enjoy lobster's pure flavor than to have it boiled and
Many fishermen switched to lobster as winter flounder, a cold-water fish once
  abundant in fishing boat holds, declined.
Image for lobster
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