Space traveller needs oxygen to revive (4,2)
I believe the answer is:
come to
'revive' is the definition.
(I know that revive can be written as come to)
'space traveller needs oxygen' is the wordplay.
'space traveller' becomes 'comet' (object travelling through space).
'needs' says to put letters next to each other.
'oxygen' becomes 'O' (atomic symbol for oxygen).
'comet'+'o'='COME TO'
'to' is the link.
(Other definitions for come to that I've seen before include "Regain consciousness - stop vessel" , "Reach" , "Resuscitate" , "Regain senses or arrive at" , "Wake up" .)