An ancient army had time for a prisoner (7)
I believe the answer is:
hostage
'prisoner' is the definition.
(someone taken as a prisoner)
'an ancient army had time' is the wordplay.
'an ancient army' becomes 'host' (host is a kind of army. I am not sure about the 'ancient' bit.).
'had' says to put letters next to each other.
'time' becomes 'age' (an age is a period of time).
'host'+'age'='HOSTAGE'
'for a' is the link.
Can you help me to learn more?
(Other definitions for hostage that I've seen before include "One held for money" , "Detainee - gash toe (anag)" , "She-goat (anag)" , "Prisoner - pawn" , "Prisoner kept as security" .)