Answer:

vapor

Answer	Crossword Clue
VAPOR	Trail behind an airplane
VAPOR	E-cigarette byproduct
VAPOR	Humidifier output

VAPOR	Word with lock or trail
VAPOR	Mist
VAPOR	Steam or mist
VAPOR	Steam
VAPOR	Something in the air
VAPOR	Type of trail
VAPOR	Jet trail
VAPOR	Gaseous mist

VAPOR	Smoke or mist
VAPOR	Kind of trail or lock
VAPOR	Steam, for example
VAPOR	Gas you can see
VAPOR	Trail type
VAPOR	Fog, mist, or steam
VAPOR	Kind of lock or trail
VAPOR	Kind of trail

VAPOR	Fog or steam
VAPOR	Fog or mist
VAPOR	Fume
VAPOR	Gas
VAPOR	Visible gas
VAPOR	Fog
VAPOR	Steam, e.g.
VAPOR	Haze, essentially

VAPOR	Mist or fog
VAPOR	Fog, e.g.
VAPOR	Contents of an automobile cylinder.
VAPOR	Mist.
VAPOR	Steam.
VAPOR	Mist or steam.
VAPOR	Trail of a jet.
VAPOR	Explosive mixture in a cylinder.

VAPOR	... trail.
VAPOR	Jet's trail.
VAPOR	Exhalation.
VAPOR	Bluster.
VAPOR	Something transitory.