Deltoid, say, providing strength (6)
I believe the answer is:
muscle
This clue is a double definition.
'deltoid say' is the first definition.
(deltoid is a kind of muscle)
'strength' is the second definition.
(muscle can mean strength or force)
'providing' acts as a link.
(Other definitions for muscle that I've seen before include "Eg, biceps" , "Consider; gaze at" , "Fibrous tissue in the body" , "Part of the body which produces movement" , "for bearing around?" .)