The term ITSY-BITSY BIT is composed of four crossword solutions: ATOM, IOTA, and two words with four letters each. ATOM refers to the smallest particle of an element that can exist, while IOTA is the ninth letter of the Greek alphabet. The two four-letter words are 'itsy' and 'bitsy, ' which are both adjectives meaning very small or tiny. Together, these four words form the phrase 'itsy-bitsy bit, ' which is a humorous way of saying something is extremely small.