E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Thrall.
A slave; bondage; wittily derived from drill, in allusion to the custom of drilling the ear of a slave in token of servitude, a custom common to the Jews. (Deut. xv. 17.) Our Saxon forefathers used to pierce at the church-door the ears of their bond-slaves. (Anglo-Saxon, thrael, slave or bondman.)
