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 .
Origin
Greek-ad- (stem of -as), specialization of feminine adjective-forming suffix, often used substantively
Anatomy, Zoology. a suffix forming adverbs from nouns signifying parts of the body, denoting a direction toward that part: dextrad; dorsad; mediad .
Origin
< Latinad toward, anomalously suffixed to the noun; introduced as a suffix by Scottish anatomist John Barclay (1758-1826) in 1803
British Dictionary definitions for -ad
-ad1
suffix
1.
a group or unit (having so many parts or members): triad
2.
an epic poem concerning (the subject indicated by the stem): Dunciad
Word Origin
via Latin from Greek -ad- (plural -ades), originally forming adjectives; names of epic poems are all formed on the model of the Iliad
-ad2
suffix
1.
denoting direction towards a specified part in anatomical descriptions: cephalad
Word Origin
from Latin ad to, towards
Word Origin and History for -ad
word-forming element denoting collective numerals (cf. Olympiad), plant families, and names of poems, from Greek -as (genitive -ados), a suffix forming fem. nouns; also used in fem. patronymics (Dryad, Naiad, also, in plural, Pleiades, Hyades).