Answer: gumup

AnswerCrossword Clue
GUMUP

Ruin

GUMUP

Spoil, slangily

GUMUP

Spoil, in slang

GUMUP
... the works (slow things down)
GUMUP
Spoil
GUMUPBungle
GUMUPRuin, informally
GUMUPClog