But it is an annoying ambiguity in English. You would probably say that curry paste is spicy even it had no capsaicin, which does happen. People also mean "has spices" when they say "spicy". I have heard Russians use the word Russian word "bitter" to describe the pain sensation of capsaicin too.

I prefer the Spanish word "picante" - stingy. It stings, it causes pain. It's not a flavour like a spice would be.

If you're expecting English words to have a single meaning, you're in for a rough time.

The problem is that there just isn't a good English word to distinguish it, I have to explain every time that I don't mean flavour, I mean pain. (Russian also has this problem, ambiguity is in every natural language.)

What word have you heard used to describe spicy food? I have only come across острая which is "sharp".

I have heard older Soviet Russians use the word горко, but this was about ten years ago. They were trying to express that the food tasted bad and they really just called it bitter when they meant it had capsaicin.