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astylar
ASU
Asunción
asunder
asura
ASV
Asvina
Aswan
aswarm
aswirl
aswoon
ASX
asyllabic
asylum
asylum seeker
asymmetric
asymmetric information
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astronomical twilight
as·tro·nom·i·cal twi·light (plural as·tro·nom·i·cal twi·lights)


noun 
Definition:
 
period when Sun just below horizon: the period of time during which the Sun is at 18º below the horizon
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