Power of second crew (5)
I believe the answer is:
Here is my best explanation:
'power' is the definition.
'second crew' is the wordplay.
'second' becomes 's' (common abbreviation).
'crew' becomes 'team' (I've seen this before).
'of' is the link.
(Other definitions for steam that I've seen before include "Mates (anag)", "Letter opener", "comes with a hiss?", "cook", "Gas from boiling water", "Vapour; energy", "Water at boiling temperature diffused in the atmosphere", "fume", "Source of energy" and "It's water mist, mates".)