nut up

Etymology 1
(influenced by expressions like "man up" or "shut up"; "nut" refers to testicles, symbolically implying being more manly)

Verb

 * 1)  To show courage and hide one's apprehension.

Usage notes

 * Often used in the imperative form, sometimes in the phrase "nut up or shut up".

Etymology 2
, apparently related to and.

Verb

 * 1)  To lose one's temper, go nuts.