Where does the term “banana oil” come from and What does banana oil mean?

Actually an aromatic liquid having the odor of a ripe banana, chiefly employed as a solvent for lacquers.

Chemically it is isoamyl acetate, if you know what that is.

But when your young son says, “Aw, that’s just banana oil,” in terms of derision or of praise, his slang usage is that he regards the “that” as either nonsense or as flattery.