One engaged by complicated devices for settling an issue? (8)
I believe the answer is:
decisive
'settling an issue?' is the definition.
(I've seen this before)
'one engaged by complicated devices' is the wordplay.
'one' becomes 'i' (Roman numeral).
'engaged by' is an insertion indicator (I've seen this in other clues).
'complicated' indicates anagramming the letters (a complex or confusing ordering of the letters).
'devices' with letters rearranged gives 'decisve'.
'i' going inside 'decisve' is 'DECISIVE'.
'for' acts as a link.
(Other definitions for decisive that I've seen before include "Able to make up one's mind quickly and with firmness" , "Critical" , "Settling something conclusively, as battle may be" , "Producing a definite result" , "Showing clear judgment and firmness" .)