juice vs lemon juice

juice and lemon juice both are nouns.

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

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

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

Other hyponyms of juice include gravy, pan gravy, lime juice, papaya juice, tomato juice, carrot juice, V-8 juice.

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