Charlie moving about, working for firm (4,4)
I believe the answer is:
cast iron
'firm' is the definition.
(I've seen this before)
'charlie moving about working' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'moving about' becomes 'astir' (astir means stirring or moving).
'working' becomes 'on' (on can mean working or activated).
'c'+'astir'+'on'='CAST-IRON'
'for' acts as a link.
(Other definitions for cast iron that I've seen before include "Secure" , "rigid" , "Solid, robust" , "Brittle alloy" , "Certain" .)