Secret rival is a term used to describe a person or group that is in competition with another, but their presence is unknown. The crossword solutions for the term are SURE (4 letters), ARRID (5 letters), and BAN (3 letters). SURE is an adjective meaning certain or definite, ARRID is an adjective meaning dry or harsh, and BAN is a verb meaning to forbid or prohibit. Together, these words can be interpreted to mean that a secret rival is someone who is certain, dry, and forbidden.