The term 'backdoor' is used to describe a HIDDEN or SECRET entrance or way of doing something, usually in an ILLICIT or SNEAKY manner. The crossword solutions for this term include 'SECRET' (6 letters), 'HIDDEN' (6 letters), 'UNDERHAND' (9 letters), 'ILLICIT' (7 letters), 'SNEAKY' (6 letters), 'CLANDESTINE' (11 letters), and 'backstairs' (10 letters) and 'POSTERN' (7 letters). All of these words are related to the idea of a backdoor, as they all imply a HIDDEN or SECRET way of doing something.