thorn [OE] One of the earliest recorded Old English words, first found before ad 700. A thorn in the side or thorn in the flesh is a source of continual annoyance or trouble. Both expressions are of biblical origin. The Old Testament book of Numbers has a verse which reads: ‘Those which ye let remain of them shall be pricks in your eyes, and thorns in your sides, and shall vex you in the land wherein ye dwell.’ In the New Testament the Second Epistle to the Corinthians has: ‘And lest I should be exalted above measure through the abundance of the revelations, there was given to me a thorn in the flesh, the messenger of Satan to buffet me.’ See also rose.