Well, I've always referred tho these as jet streams or jet trails, and never realized there was a specific term/word for it until someone mentioned it on The Weather Channel today while pointing out that contrails now account for a measurable percentage of the cloud cover. Only got one hit on OneLook, so here it is...has anybody heard this before. And, since there's no date of origin, can anybody pinpoint a time of coinage? Perhaps it was used in the official aviation lingo from the introduction of jet aircraft? But the lack of documentation would seem to suggest it's coinage is fairly recent. The etymology is pretty simple: condensation plus trail = contrail:

from the American Heritage dictionary

con·trail (kntrl)
n.
A visible trail of streaks of condensed water vapor or ice crystals sometimes forming in the wake of an aircraft. Also called vapor trail.

------------------------------------------------------------[con(densation) trail.]