ETYMOLOGY
from Latin ūnus one + asinus ass, after unanimous
FIRST DOCUMENTED USE
1656 – see EXAMPLE below
EXAMPLE
“…Go your wayes,” says he to Dr Wallis and Seth Ward, you uncivil Ecclesiastiques, inhyman divines, Dedoctors of Morality, Unasinous collegues, Egregious pair of Issachars, most wretched Vindices and Indices Academarium….”
From: Elements of Philosophy the First Section, Concerning Body,
Wwritten in Latine by Thomas Hobbes of Malmesbury;
And now translated into English;
To which are added Six lessons to the Professors of Mathematicks of the Institution of Sr. Henry Savile, in the University of Oxford
Lexicophilia 