An Etymological Dictionary of Astronomy and Astrophysics

1. The act of agreeing or of coming to a mutual arrangement.
   

2. The state of being in accord (Dictionary.com).

Etymology (EN): Verbal noun from → agree + → -ment.

Etymology (PE): Sâcan, from sâz-, saz, sac-, sâj-, Pers. sâz-, sâxtan “to build, prepare; to agree, be compatible; to adapt, adjust;” sazidan “to suit, fit, be worthy,” sazâ “suitable, agreeing with, congruous, deserving of;” Baluchi sâc-/sâcit “to adjust, be suitable, agree;” Mid.Pers. sacitan/sazidan “to fit,” sazešn “fitness,” sazâg “fitting, worth;” Av. sak- “to understand, to mark,” sâcaya- (causative) “to teach;”
Proto-Ir. *sac- “to fit, be suitable; to prepare;” + suffix -an, → minus.