knife-edge
Concise Oxford English Dictionary © 2008 Oxford University Press:
knife-edge
▶noun
- 1 the cutting edge of a knife.
■ [as modifier] (of creases or pleats) very fine.
- 2 a very tense or dangerous situation.
- 3 a steep mountain ridge; an arête.
- 4 a steel wedge on which a pendulum or other device oscillates or is balanced.
'knife-edge' also found in these Oxford entries:

