lemon juice vs juice

lemon juice and juice both are nouns.

Word	Noun	Adjective	Verb	Adverb
lemon juice	Yes	No	No	No
juice	Yes	No	No	No

As nouns, juice is a hypernym of lemon juice; that is, juice is a word with a broader meaning than lemon juice:

lemon juice: usually freshly squeezed juice of lemons
juice: the liquid part that can be extracted from plant or animal tissue by squeezing or cooking

lemon juice (noun)	juice (noun)
usually freshly squeezed juice of lemons	any of several liquids of the body
	the liquid part that can be extracted from plant or animal tissue by squeezing or cooking
	electric current
	energetic vitality