Similar to b.d./b.i.d.

a.d. - auris dextra - right ear
a.l., a.s. - auris laeva, auris sinistra - left ear
a.m. - ante meridiem - morning, before noon
A.T.C. - around the clock
a.u. - auris utraque - both ears
aa - ana - of each
ad - ad - up to

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