Piquant is a legitimate but rarely used English word which means "a pleasing irritation or pungent taste sensation" (from French piquer, to prick). The term "hot" is commonly misused for describing the taste sensation caused by capsaicin, the pungent component of Capsicum (chile). Because the irritation produced by this compound produces a "burning" sensation, we sloppily use a term associated with temperature. But using "hot" in this sense is as incorrect as using "cold" to describe the taste of peppermint, which is also caused by irritation.
Temperature descriptions for irritation should be avoided, especially when a perfectly good, accurate term is available, since temperature and seasoning are two very important and distinct considerations in food preparation.
Why harp on this? Because the wrong term unnecessarily creates ambiguity and confusion. If a sauce is "too hot," is it "too hot" or "too spicy" (another unfortunate term)? Yet the term "picante sauce" has a clear unambiguous connotation. Spanish speakers use the correct term -- picante. Why can't we use the correct English word -- piquant?
"Pungent" encompasses piquancy, but includes also the olfactory irritation caused by mustard or horseradish, which do not contain capsaicin. "Spicy" means what it says, but not necessarily pungency.