Soldier perhaps catching disease far away (6)
I believe the answer is:
absent
'far away' is the definition.
'soldier perhaps catching disease' is the wordplay.
'soldier perhaps' becomes 'ant' (soldier is a type of ant).
'catching' means one lot of letters goes inside another.
'disease' becomes 'bse' (bovine spongiform encephalopathy, mad cow disease).
'ant' enclosing 'bse' is 'ABSENT'.
(Other definitions for absent that I've seen before include "nowhere to be seen" , "lack of attention" , "Forgetful, with mind on other things" , "Inattentive" , "Not at a specified place" .)