one wanting in courage; a coward ...a1627 obs.
from quake + buttock
FIRST DOCUMENTED USE
a1627 - see EXAMPLE below
"...Much like the Art of swimming, he that will attain to't
Must fall Plump, and duck himself at first,
And that will make him hardy and advent'rous,
And not stand putting in one Foot, and shiver,
And then draw t'other after, like a quake-buttock;..."
From: Comedies and Tragedies
Francis Beaumont and John Fletcher
Wit at Severall Weapons