Answer:

RSVP

Answer	Crossword Clue
RSVP	Invitation letters
RSVP	Respond to an invitation
RSVP	Call-back request

RSVP	SASE answer
RSVP	Invitation request
RSVP	Party giver's abbr.
RSVP	Reply, as to an event invitation
RSVP	Answer an invitation
RSVP	"Regrets only" alternative
RSVP	Letters needing reply
RSVP	Alert the host

RSVP	Notify the host
RSVP	Host's request
RSVP	Invitation initialism
RSVP	Evite request
RSVP	"Please answer," on an invitation
RSVP	Party invitation request
RSVP	Request to an invitee
RSVP	"Let me know," on an invitation

RSVP	Answer, briefly
RSVP	It may be followed by a phone no.
RSVP	"Let us know," initially
RSVP	Letters before a phone no., maybe
RSVP	"Let us know if you're coming" letters
RSVP	"Let us know," on an invitation
RSVP	"Please answer"
RSVP	It may involve regrets

RSVP	Letters before a phone no., perhaps
RSVP	Part of a prospective bride's pile
RSVP	Request from a party leader
RSVP	Abbr. on an invitation
RSVP	It may consist of regrets
RSVP	Letters sometimes preceding a phone no.
RSVP	"Let us know," to an invitee
RSVP	SASE contents, perhaps

RSVP	Short answer?
RSVP	Brief answer?
RSVP	Answer an invite
RSVP	Let us know, in an invite
RSVP	Letters on reply cards