Clue: Tenor misses opening of Götterdämmerung, a dotty little thing (6)
Answer: DOMINO
Explanation: Definition: a dotty little thing
A subtraction: DOMIN[g]O (Plácido, 'tenor' for most of his career, although now more of a baritone) minus the G ('missing the opening of **G**ötterdämmerung'),with a cryptic definition.