Easton's Bible Dictionary (1897)
An instrument only referred to in connection with the custom of boring the ear of a slave (Ex. 21:6; Deut. 15:17), in token of his volunteering perpetual service when he might be free. (Comp. Ps. 40:6; Isa. 50:5).
Smith's Bible Dictionary (1863)
a tool of which we do not know the ancient form. The only notice of it is in connection with the custom of boring the ear of the slave.