dipstick

Short definition from Wiktionary

Noun

1. 1
   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.
2. 2
   An exciseman or supervisor who measures with a dipstick.
3. 3
   The penis.
4. 4
   A useless person of inferior intellect; a dipshit.

Verb

1. 1
   To check (a person) for their understanding of something, as of a lesson, or attitude toward something.
2. 2
   To measure the level of a fluid using a dipstick.