An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Not clearly or explicitly stated or expressed.
2) Indefinite or indistinct in nature or character, as ideas or feelings.
3) Not definitely established, determined, confirmed, or known; uncertain (Dictionary.com). → ambiguous, → nebulous, → indefinite, → fuzzy, → unclear.

M.E., from M.Fr. vague "empty, vacant; wild, uncultivated; wandering," from L. vagus "wandering, rambling," of unknown origin.

Gereng, from Kalidari gereng "wandering," Kurd. (Kurmanji) garin, (Sorani) garân "to wander," Dehxodâ gereng "shattered;" ultimately from Proto-Ir. *gar-an-ka-, from *gar- "to turn, to wind" (Cheung 2007).

A year of 365 days that overlooks the fraction of less than 0.25 days corresponding to the whole length of the → tropical year. The vague year was used in the → calendars of ancient Egypt, Iran, Mayas, and some other civilizations. Typically the vague year was divided into 12 months of 30 days each plus 5 → epagomenal days.

From annus vagus "wandering year;" → vague→ year.