An Etymological Dictionary of Astronomy and Astrophysics

1. Appropriate, favorable, or suitable.
   

2. Occurring or coming at an appropriate time; well-timed (Dictionary.com).

Etymology (EN): 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.”

Etymology (PE): 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.