detune
Concise Oxford English Dictionary © 2008 Oxford University Press:
detune/diːˈtjuːn/
▶verb
- 1 cause (a musical instrument) to become out of tune.
- 2 (usu. as adj. detuned) reduce the performance of (a motor vehicle or engine) by adjustment.
- 3 change the frequency of (an oscillatory system such as a laser) away from a state of resonance.
'detune' also found in these Oxford entries:

