-ad²

Indicating a direction towards some part of the body.

Latin ad, to or towards.

A set of adverbs was invented in 1803 by the Scottish anatomist John Barclay (1758–1826) in his book A New Anatomical Nomenclature; he created them from adjectives in ‑al (see ‑al¹) by replacing that ending with ‑ad, so for example making ventrad, towards the abdominal surface of the body, from ventral. They are specialist words, mainly confined to zoology. Two further examples are cephalad (Greek kephalē, head), towards the head, and caudad (Latin cauda, tail), towards the tail.