The term UNFORGETTABLE SINGER can be solved by the crossword solutions COLE (4 letters), NAT (3 letters), and NATKINGCOLE (11 letters). Cole is a reference to the iconic singer, Nat King Cole, who was known for his smooth baritone voice and jazz-influenced music. His most famous songs include 'UNFORGETTABLE, ' 'Mona Lisa, ' and 'SMILE.' Nat is a shortened version of his name, Nat King Cole. NatKingCole is the full name of the singer.