white whale vs Delphinapterus leucas

white whale and Delphinapterus leucas both are nouns.

Word	Noun	Adjective	Verb	Adverb
white whale	Yes	No	No	No
Delphinapterus leucas	Yes	No	No	No

As nouns, white whale and Delphinapterus leucas are synonyms defined as:

white whale and Delphinapterus leucas: small northern whale that is white when adult

Other synonyms of white whale include beluga.

white whale (noun)	Delphinapterus leucas (noun)
small northern whale that is white when adult	small northern whale that is white when adult