saliva vs tobacco juice

saliva and tobacco juice both are nouns.

Word	Noun	Adjective	Verb	Adverb
saliva	Yes	No	No	No
tobacco juice	Yes	No	No	No

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

saliva: a clear liquid secreted into the mouth by the salivary glands and mucous glands of the mouth; moistens the mouth and starts the digestion of starches
tobacco juice: saliva colored brown by tobacco (snuff or chewing tobacco)

Other hyponyms of saliva include dribble, drivel, drool, slobber.

saliva (noun)	tobacco juice (noun)
a clear liquid secreted into the mouth by the salivary glands and mucous glands of the mouth; moistens the mouth and starts the digestion of starches	saliva colored brown by tobacco (snuff or chewing tobacco)