Part of circle in rescue vessel, do we hear? (3)
I believe the answer is:
arc
'part of circle' is the definition.
(part of the circumference of a circle)
'rescue vessel do we hear?' is the wordplay.
'rescue vessel' becomes 'ark' (rescue ship in the Bible).
'do we hear?' indicates a 'sounds like' (homophone) clue.
'ark' is a homophone of 'ARC'.
'in' is the link.
(Other definitions for arc that I've seen before include "Part of a circular line" , "development of plot" , "Part of a circle's circumference" , "Don't go straight" , "Segment of circumference" .)