Meaning of -AD in English
1. a suffix occurring in loanwords from Greek denoting a group or unit comprising a certain number, sometimes of years: dyad; triad.
2. a suffix meaning "derived from," "related to," "concerned with," "associated with" ( oread ), introduced in loanwords from Greek ( Olympiad; oread ), used sporadically in imitation of Greek models, as Dunciad, after Iliad.
[ Gk -ad- (s. of -as ), specialization of fem. adjective-forming suffix, often used substantively ]
var. of -ade 1 : ballad.
Anat., Zool. a suffix forming adverbs from nouns signifying parts of the body, denoting a direction toward that part: dextrad; dorsad; mediad.
[ ad toward, anomalously suffixed to the noun; introduced as a suffix by Scottish anatomist John Barclay (1758-1826) in 1803 ]
Random House Webster's Unabridged English dictionary. Полный английский словарь Вебстер - Random House . 2012