Answer:

crasher

Answer	Crossword Clue
CRASHER	Unwelcome guest
CRASHER	Intruder: Slang.
CRASHER	Uninvited attendee

CRASHER	Uninvited partygoer
CRASHER	Uninvited party guest
CRASHER	Uninvited wedding guest

Crossword

a puzzle consisting of a grid of squares and blanks into which words crossing vertically and horizontally are written according to clues.