Feminine suffixes are a set of four common endings used to denote femininity in words. These suffixes are ennes (5 letters), ines (4 letters), ettes (5 letters), and inas (4 letters). They are typically added to the end of nouns, adjectives, and verbs to indicate that the word is feminine. For example, the word 'prince' can be changed to 'PRINCESS' by adding the suffix '-ess'. Similarly, the word 'HERO' can be changed to 'HEROINE' by adding the suffix '-ine'.