Answer: sisisenor

AnswerCrossword Clue
SISISENOR

Sylvester's least favorite Spanish agreement?

SISISENOR

Emphatic affirmative, in Acapulco

SISISENOR

Emphatic south-of-the-border assent

SISISENOR
A south-of-the-border assent
SISISENOR
Acapulco assent (and a phonetic hint to four of the Across answers)