word-forming element meaning "best," also "of the aristocracy," from Greek aristos "best of its kind, noblest, bravest, most virtuous" (of persons, animals, things), originally "most fitting," from PIE *ar(ə)-isto-, suffixed (superlative) form of root *ar- "to fit together."
word-forming element meaning "arterial," from Latinized form of Greek arteria "windpipe; artery" (see artery).
before vowels arth-, word-forming element meaning "pertaining to the joints," from Greek arthron "joint," from PIE *ar(ə)-dhro-, suffixed form of root *ar- "to fit together."
assimilated form of ad- "to, toward, before" before stems beginning in -t-; see ad-. In Old French and Middle English regularly reduced to a-, later restored.
word-forming element meaning "one quintillionth," 1962, from Danish atten "eighteen" (a quintillion is 10 to the 18th power), related to Old English eahtatene (see eighteen).
word-forming element meaning "sound, hearing," from combining form of Latin audire "to hear" (from PIE root *au- "to perceive"); used in English word formation by 1890s.