spanner
Concise Oxford English Dictionary © 2008 Oxford University Press:
spanner/ˈspanə(r)/
▶noun chiefly Brit. a tool with a shaped opening or jaws for gripping and turning a nut or bolt.
– phrases
a spanner (or N. Amer. monkey wrench) in the works a person or thing that prevents the successful implementation of a plan.
a spanner (or N. Amer. monkey wrench) in the works a person or thing that prevents the successful implementation of a plan.
'spanner' also found in these Oxford entries:

