crab vs Alaska crab

crab and Alaska crab both are nouns.

Word	Noun	Adjective	Verb	Adverb
crab	Yes	No	Yes	No
Alaska crab	Yes	No	No	No

As nouns, Alaska crab is a hyponym of crab; that is, Alaska crab is a word with a more specific, narrower meaning than crab:

crab: decapod having eyes on short stalks and a broad flattened carapace with a small abdomen folded under the thorax and pincers
Alaska crab: large edible crab of northern Pacific waters especially along the coasts of Alaska and Japan

As nouns, Alaska crab is a hyponym of crab; that is, Alaska crab is a word with a more specific, narrower meaning than crab:

crab (noun)	Alaska crab (noun)
a stroke of the oar that either misses the water or digs too deeply	large edible crab of northern Pacific waters especially along the coasts of Alaska and Japan
decapod having eyes on short stalks and a broad flattened carapace with a small abdomen folded under the thorax and pincers	meat of large cold-water crab; mainly leg meat
a louse that infests the pubic region of the human body
the edible flesh of any of various crabs
a quarrelsome grouch

crab (verb)	Alaska crab (verb)
complain
fish for crab
scurry sideways like a crab
direct (an aircraft) into a crosswind