Wooded area once part of Arthur's territory (5)
I believe the answer is:
hurst
'wooded area' is the definition.
(archaic term for a wood)
'part of arthur's territory' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'HURST' can be found hidden inside 'arthurs territory'.
'once' acts as a link.
(Other definitions for hurst that I've seen before include "World Cup hero" , "A few ashes maybe" , "wood" , "Grove" , "Wooded rise (archaic)" .)