Proto-Indo-European root meaning "to, near, at."
It forms all or part of: abate; ado; ad-; ad hoc; ad lib; adage; adagio; add; adjective; adore; adorn; adult; adverb; advertise; agree; aid; alloy; ally; amontillado; amount; assure; at; atone; exaggerate; paramount; rapport; twit.
It is the hypothetical source of/evidence for its existence is provided by: Sanskrit adhi "near;" Latin ad "to, toward;"
Old English æt.
acupuncturist
acute
-acy
ad
ad-
*ad-
-ad
ad hoc
ad hominem
ad infinitum
ad lib