A stick or rod used to measure the depth of a liquid. Often used to check the level at which a liquid in an opaque or inaccessible tank or reservoir stands; gauge.
I haven't checked the oil level of my car's motor since I lost the dipstick three months ago.
A penis.
A useless person of inferior intellect; a dipshit.
That referee is a right dipstick.
To check (a person) for their understanding of something, as of a lesson, or attitude toward something.