River and wood crossing area in kingdom (5)
I believe the answer is:
realm
'kingdom' is the definition.
(kingdom is a type of country or realm)
'river and wood crossing area' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'and' is a charade indicator (letters next to each other).
'wood' becomes 'elm' (elm is a type of tree).
'crossing' indicates putting letters inside.
'area' becomes 'a' (maths abbreviation).
'elm' going around 'a' is 'ealm'.
'r'+'ealm'='REALM'
'in' is the link.
(Other definitions for realm that I've seen before include "Knowledge base" , "World" , "King's domain" , "region" , "Kingdom or sphere" .)