touch off

Verb

touch off (third-person singular simple present touches off, present participle touching off, simple past and past participle touched off)

1. (idiomatic, transitive) 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, transitive) To cause a fire to start.
   • A spark touched off the conflagration.
3. 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.