Nothin' Doin' is an American slang phrase used to express a lack of enthusiasm or interest in something. It is often used as a response to a suggestion or invitation, and can be interpreted as a polite way of declining. The two crossword solutions for this phrase are 'NAH' (3 letters) and 'UHUH' (4 letters). Both of these words are informal versions of 'NO' and can be used to express the same sentiment.