What is the definition of English word icasm?

There is no English word "icasm". It seems like you may be looking for a word like "irony" or "sarcasm", both of which involve using language in a way that is different from its literal meaning.

* Irony refers to a situation where the outcome is the opposite of what was expected, often with a humorous or tragic effect.

* Sarcasm is a form of verbal irony that is intended to be hurtful or mocking.

If you can give me more context about how you came across the word "icasm," I may be able to help you find the word you're looking for.