Vapour (5)
'vapour' is the definition.
(steam is a kind of vapour)
This is all the clue.
(Other definitions for steam that I've seen before include "Invisible gas from boiling water" , "get very angry" , "It's water mist, mates" , "Vapourised water" , "Old-fashioned power" .)
'vapour' is the definition.
(smoke is a kind of vapour)
This is the entire clue.
(Other definitions for smoke that I've seen before include "'There's no . . . . . without fire'" , "Cigarette or cigar (colloq.)" , "Visible vapour" , "Cure (meat) over fire" , "Carbon vapour" .)
'vapour' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for gas that I've seen before include "Something that is neither solid not liquid" , "may fill American car" , "Hydrogen or methane, say" , "Talk profusely" , "American fuel" .)