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

1) Appropriate, favorable, or suitable.
2) Occurring or coming at an appropriate time; well-timed (Dictionary.com).

M.E., from O.Fr. opportun and directly from L. opportunus "fit, convenient, suitable," from the phrase ob portum veniens "coming toward a port," literally "a wind blowing to harbor," from ob "to, toward" + portus "access, harbor."

Nikvâ "appropriate, suitable," from nik, nêk, neku "good, beautiful, elegant;" Mid.Pers. nêk, nêvak, nêkôg "good, beautiful;" O.Pers. naiba- + -vâ relation suffix (as in pišvâ, pilévâ); alternatively, nikvâ "good/appropriate wind," from nik + vâ "wind," variant of bâd, → wind, in several dialects.