Hit rain, travelling: disappeared into it? (4,3)
I believe the answer is:
thin air
'disappeared into it?' is the definition.
(as in disappearing into thin air)
'hit rain travelling' is the wordplay.
'travelling' indicates anagramming the letters.
'hit'+'rain'='hitrain'
'hitrain' with letters rearranged gives 'THIN AIR'.
(Other definitions for thin air that I've seen before include "Vanish into . . . . . . ., say high on Everest" , "To vanish into this is to become invisible" , "Vanish completely as into . . . . . . ., on high mountain?" , "Nothingness into/from which things might magically (dis)appear" , "Things seem to vanish into this" .)