Main Difference
The main difference between Crab and Lobster is that the Crab is a infraorder of crustaceans and Lobster is a family of crustaceans.
Crab
Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting “tail” (abdomen) (Greek: βραχύς, romanized: brachys = short, οὐρά / οura = tail), usually entirely hidden under the thorax. They live in all the world’s oceans, in fresh water, and on land, are generally covered with a thick exoskeleton and have a single pair of pincers. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs.
Lobster
Lobsters are a family (Nephropidae, sometimes also Homaridae) of large marine crustaceans.
Lobsters have long bodies with muscular tails, and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, including the first pair, which are usually much larger than the others. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate. Commercially important species include two species of Homarus (which looks more like the stereotypical lobster) from the northern Atlantic Ocean, and scampi (which looks more like a shrimp, or a “mini lobster”) – the Northern Hemisphere genus Nephrops and the Southern Hemisphere genus Metanephrops. Although several other groups of crustaceans have the word “lobster” in their names, the unqualified term “lobster” generally refers to the clawed lobsters of the family Nephropidae. Clawed lobsters are not closely related to spiny lobsters or slipper lobsters, which have no claws (chelae), or to squat lobsters. The closest living relatives of clawed lobsters are the reef lobsters and the three families of freshwater crayfish.
Crab (noun)
A crustacean of the infraorder Brachyura, having five pairs of legs, the foremost of which are in the form of claws, and a carapace.
Crab (noun)
The meat of this crustacean, served as food; crabmeat
Crab (noun)
A bad-tempered person.
Crab (noun)
An infestation of pubic lice (Pthirus pubis).
“Although crabs themselves are an easily treated inconvenience, the patient and his partner(s) clearly run major STD risks.”
Crab (noun)
A playing card with the rank of three.
Crab (noun)
A position in rowing where the oar is pushed under the rigger by the force of the water.
Crab (noun)
A defect in an outwardly normal object that may render it inconvenient and troublesome to use.
Crab (noun)
The crab apple or wild apple.
Crab (noun)
The tree bearing crab apples, which has a dogbane-like bitter bark with medical use.
Crab (noun)
A cudgel made of the wood of the crab tree; a crabstick.
Crab (noun)
A movable winch or windlass with powerful gearing, used with derricks, etc.
Crab (noun)
A form of windlass, or geared capstan, for hauling ships into dock, etc.
Crab (noun)
A machine used in ropewalks to stretch the yarn.
Crab (noun)
A claw for anchoring a portable machine.
Crab (noun)
The tree species noshow=1, native of South America.
Crab (noun)
Short for carabiner.
Crab (verb)
To fish for crabs.
Crab (verb)
To ruin.
Crab (verb)
To complain.
Crab (verb)
To drift or move sideways or to leeward by analogy with the movement of a crab.
Crab (verb)
To navigate (an aircraft, e.g. a glider) sideways against an air current in order to maintain a straight-line course.
Crab (verb)
, to fly slightly off the straight-line course towards an enemy aircraft, as the machine guns on early aircraft did not allow firing through the propeller disk.
Crab (verb)
To back out of something.
Crab (verb)
(obsolete) To irritate, make surly or sour
Crab (verb)
To be ill-tempered; to complain or find fault.
Crab (verb)
(British dialect) To cudgel or beat, as with a crabstick
Lobster (adjective)
red-colored, especially from a sunburn.
Lobster (noun)
A crustacean of the Nephropidae family, dark green or blue-black in colour turning bright red when cooked, with a hard shell and claws, which is used as a seafood.
Lobster (noun)
A crustacean of the Palinuridae family, pinkish red in colour, with a hard, spiny shell but no claws, which is used as a seafood.
Lobster (noun)
A soldier or officer of the imperial British Army (due to their red or scarlet uniform).
Lobster (noun)
An Australian twenty dollar note, due to its reddish-orange colour.
Lobster (verb)
To fish for lobsters.