touch off
verb1
Idiomatic To start (something); to set off traps; especially used for unstable situations that may magnify if disturbed.
- Be cautious talking about religion or politics, lest you touch off an argument.
2
Idiomatic To cause a fire to start.
- A spark touched off the conflagration.
3
Engineering, Machining, Mechanical engineering, Natural sciences, Physical sciences To establish a reference coordinate or datum, by moving the tool head to just touch the workpiece or machine bed.
- A traditional method of touching off uses a piece of thin paper placed between the tool and workpiece.