The crossword solution for the term 'Ordinal Number Suffix' is ETH, which is a three-letter suffix. This suffix is used to denote an ordinal number, which is a number that indicates position or rank in a sequence. For example, the suffix -eth is added to the end of cardinal numbers (numbers that indicate quantity) to form ordinal numbers. For instance, the cardinal number 'five' becomes 'fifth' when the suffix -eth is added.