Island location army conceals (4)
I believe the answer is:
iona
'island' is the definition.
(I've seen this before)
'location army conceals' is the wordplay.
'conceals' indicates the answer is hidden within the clue.
'IONA' is hidden within 'location army'.
(Other definitions for iona that I've seen before include "Isle of the Inner Hebrides, made famous by St Columba" , "Macbeth's resting" , "part of Scotland" , "Saint Columba's isle" , "Scottish land known for St Columba" .)