The term 'COMPARATIVE SUFFIX' refers to a type of suffix that is used to compare two things. The three crossword solutions for this term are MERRIER (7 letters), IER (3 letters), and IOR (3 letters). These suffixes are added to adjectives or adverbs to create comparative forms, such as 'HAPPIER' or 'FASTER'. For example, the suffix 'IER' can be added to the adjective 'HAPPY' to create the comparative form 'HAPPIER'. Similarly, the suffix 'IOR' can be added to the adverb 'FAST' to create the comparative form 'FASTER'. The suffix 'MERRIER' is an alternative form of 'IER' and can also be used to create comparative forms.