Monster books useful for firefighters (7)
I believe the answer is:
hydrant
'useful for firefighters' is the definition.
I can't tell whether this defines the answer.
'monster books' is the wordplay.
'monster' becomes 'Hydra' (Hydra is an example).
'books' becomes 'NT' (abbreviation for New Testament).
'hydra'+'nt'='HYDRANT'
Can you help me to learn more?
(Other definitions for hydrant that I've seen before include "Fire hose supplier" , "Firemen's water supply" , "Main connection" , "Water-supplier for fire-fighters" , "Upright water pipe in the street" .)