If someone is all keyed up, he is anxious or nervous, usually in anticipation of something. The expression keyed up first came into use in the 1880s and is derived from the field of music. To key up something means to tune an instrument to a particular key.

What does the saying keyed up mean?

informal. : in a state of nervous excitement His hands were very sure. He was confident he could do the work, yet inside he was keyed up and jumpy.—

What does it mean to key someone up?

key someone up

to cause someone to be anxious or excited. The excitement of the moment really keyed me up. Thoughts of their vacation keyed up the children so much they couldn't sleep. See also: key, up.