Rescue boat trapped between delta and cape in night-time (8)
I believe the answer is:
darkness
'night-time' is the definition.
'rescue boat trapped between delta and cape' is the wordplay.
'rescue boat' becomes 'ark' (rescue boat during the biblical flood).
'trapped between' means one lot of letters goes inside another.
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'and' means one lot of letters go next to another.
'cape' becomes 'ness' ('ness' can be a synonym of 'cape').
'd'+'ness'='dness'
'ark' going within 'dness' is 'DARKNESS'.
'in' acts as a link.
(Other definitions for darkness that I've seen before include "mystery" , "'Hello . . . . . . . ., my old friend' (Simon and Garfunkel song)" , "Absence of light" , "'... cannot drive out ...: only light can do that'' (Martin Luther King)" , "See 19" .)