"white line of ice crystals behind an airplane in motion," 1945, from condensation trail (1942); see condensation.
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condensation n.
c. 1600, "action or state of making or becoming more dense," from Late Latin condensationem (nominative condensatio), noun of action from past-participle stem of Latin condensare "to make dense" (see condense). Meaning "conversion of a gas or vapor to a liquid form" is from 1610s.