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astronomical unit a unit of length based on the average distance of the earth from the sun, equal to about 149.6 million kilometers or ninety-three million miles.
astronomical year a unit of time equal to the period between one vernal equinox and the next.
astronomy the branch of science concerned with the physical universe beyond the atmosphere of the earth.
astrophotography the photographing of astronomical objects.
astrophysics (used with a sing. verb) the branch of physics that deals with the physical and chemical properties of heavenly bodies and interstellar space.
astute keen in understanding and judgment; shrewd.
Asunción the capital of Paraguay.
asunder in or into separate parts or pieces. [2 definitions]
as usual in the usual way; as always.
as well in addition; also; too.
as well as and also; and moreover. [2 definitions]
as yet up until now.
asylum an institution for the care of those who are unable to maintain themselves, such as orphans or the severely mentally ill. [3 definitions]
asymmetric different, esp. in arrangement of space, on either side of a center line; not symmetrical; unbalanced.
asymmetry the state or quality of having two unidentical halves; lack of balance.
asymp tomatic not showing any symptoms of a disease (usu. used in reference to an individual who does, in fact, have the disease and may or may not be a carrier).
asymptote in mathematics, a straight line that approaches but never meets a curve.
asynchronous not occurring at the same time. [2 definitions]
At symbol of the chemical element astatine.
at1 on or in the location of. [5 definitions]
at2 the smaller monetary unit of Laos. (Cf. kip.)