Landed area in muddy surroundings for the army (8)
I believe the answer is:
military
'army' is the definition.
(thesaurus)
'landed area in muddy surroundings for' is the wordplay.
'landed' becomes 'lit' (light or alight can mean to land).
'area' becomes 'a' (maths abbreviation).
'in' indicates putting letters inside.
'muddy' becomes 'miry' (synonyms).
'surroundings for' indicates putting letters inside.
'a' inserted into 'miry' is 'miary'.
'lit' placed into 'miary' is 'MILITARY'.
'the' acts as a link.
(Other definitions for military that I've seen before include "Relating to armed forces" , "Related to soldiering" , "in the field" , "Relating to the army" , "Relating to soldiers or war" .)