listen up meaning (informal): definition

listen up

verb

Etymology From listen + up. First use appears c. 1933, although the exact date of its first use is uncertain. See cite below.

Idiomatic, Imperative, Informal, Often To listen closely; to pay attention.

Potentially derogatory

I'm only gonna say this once, so you really need to listen up.
His sharp eyes scanned the faces of his charges. "Listen up!" he barked.1933, Eddie Dooley, Under the Goal Posts:

1 more example

Listen up brothers and sisters, come hear my desperate tale. / I speak of our friends of nature, trapped in the dirt like a jail.1994, “Carrot Juice Is Murder”, in Russell's Shorts, performed by The Arrogant Worms: