The term 'Abby Sister' can be broken down into three crossword solutions: ANN (3 letters), DEAR (4 letters), and TWIN (4 letters). ANN is a female given name, derived from the Hebrew name Hannah, meaning 'GRACE' or 'FAVOR'. DEAR is an adjective used to address someone in a polite or affectionate way. TWIN is a noun that refers to two individuals who share the same parents and were born at the same time. Together, these three words form the phrase 'Abby Sister', which is used to refer to a female sibling who is both a TWIN and a DEAR friend.