Step outside steamship with awfully green travellers (10)
I believe the answer is:
passengers
'travellers' is the definition.
(passenger is a kind of traveller)
'step outside steamship with awfully green' is the wordplay.
'step' becomes 'pas' (I've seen this before).
'outside' says to put letters next to each other (outside can mean adjacent to).
'steamship' becomes 'ss'.
'with' means one lot of letters goes inside another.
'awfully' indicates an anagram.
'green' anagrammed gives 'enger'.
'ss' enclosing 'enger' is 'sengers'.
'pas'+'sengers'='PASSENGERS'
(Other definitions for passengers that I've seen before include "who'll get transferred by coach, perhaps" , "Travellers on a bus, etc" , "Weak team members" , "People on buses perhaps" .)