IF NOT' is a phrase used to express the opposite of something. It is often used in conditional statements, such as 'If not X, then Y'. The crossword solutions ELSE (4 letters), NISI (4 letters), UNLESS (6 letters), OTHERWISE (9 letters), BUT (3 letters), OR (2 letters), INLESS (6 letters), and ORELSE (6 letters) are all variations of the phrase 'IF NOT'. They are used to express the same idea, BUT with different wordings.