As a verb, to shoulder someone in the crotch. As a noun, the shouldering of someone in the crotch. Generally executed by midgets and received by NBA players.
OW!! That 6 year old just TACHED me.
He deserved a tach.
To rev an engine out past the reading capabilities of it's tachometer. This often happens in built 4 cylinder engines that have been designed to rev past normal engine limits, sometimes past 11,000 RPMs. This problem is often resolved by putting a monster5" tach on the dash. Installing this equipment is also common among ricers who want their car to seem fast.
Damn son!!! I dropped a new built b18 in my EG hatch and I tach out everytime I hit the gas!!! Honda power!!!