An Etymological Dictionary of Astronomy and Astrophysics

1. Not in a certain place at a given time; away, missing (opposed to present).
   

2. Lacking; nonexistent (Dictionary.com).

Etymology (EN): M.E., from M.Fr. absent, from L. absentem (nominative absens), p.p. of abesse “to be away from,” from → ab- “away” + esse “to be,” → present.

Etymology (PE): Apâst, on the model of L. absentem, as above, from apâ- “away from,” → apo-, + ast “is,” → present.