un-: means "not" (e.g., unhappy = not happy).in-: means "not" (e.g., incomplete = not complete).
im-: a variation of "in-" used before words starting with "m" or "p" (e.g., impossible = not possible).
il-: another variation of "in-" used before words starting with "l" (e.g., illegal = not legal).
ir-: used before words starting with "r" (e.g., irregular = not regular).
dis-: means "not" or "opposite of" (e.g., disagree = not agree).
non-: means "not" (e.g., nonsense = not making sense).
Each prefix changes the meaning of the base word to its opposite or a negated form.