ETYMOLOGY
from French aguerri, (to accustom to war) + -ed
EXAMPLE
“…But, said he, we have an army to defend us in case of an invasion; an army maintain’d in time of peace, and the best aguerried of any troops in Europe that have never seen an enemy…”
From: Letters from a Persian in England to his Friend at Ispahan
By George Lyttelton, 1735
Lexicophilia 