means A group of things considered together as a single collection, or the act of putting something in a particular place or state.

from From Old English 'settan,' meaning to cause to sit or place, a causative cousin of 'sittan' (to sit) — so to 'set' something down is literally to make it sit. The word ballooned over centuries into one of English's most overworked verbs and nouns, racking up hundreds of distinct senses; the mathematical 'set' is a much later, more abstract borrowing of that same 'things placed together' idea.