An Etymological Dictionary of Astronomy and Astrophysics

1. To state or set forth the meaning of (a word, concept, etc.).
   

2. To explain or identify the nature or essential qualities of.
   

3. To fix or mark the boundaries or extent of.

Etymology (EN): From O.Fr. définir “to end, determine,” from L. definire “to limit, determine, explain,” from → de- + finire “to bound, limit,” from finis “boundary.”

Etymology (PE): Hedâridan, infinitive from Semnâni hedâr “boundary (between pieces of lands),” Tabari hedâri “boundary, border,” may be related to
Av. haêtav- “dam, dike,” Skt. setu- “a ridge of earth, bank, dike, dam, bridge.”