1. Ichidan verb, Intransitive verb

   to be clear (of a sight, sound, colour, etc.); to be bright; to be vivid; to be crisp

   満月が空にさえている。

2. to be clear-headed; to be alert; to be on the ball; to be wide awake

3. to look upbeat; to be perky; to be cheerful

   often as 冴えない

4. to master (a skill); to excel at; to cleanly execute

5. to be satisfying

   often as 冴えないsee 冴えない

6. to become frigid; to become intensely cold

   original meaning; now somewhat old-fashioned

Also written 冱える【さえる】saeru