Bleak loch in storm — nothing escapes it (5,4)
I believe the answer is:
black hole
'nothing escapes it' is the definition.
(nothing can escape from a black hole)
'bleak loch in storm' is the wordplay.
'in storm' indicates anagramming the letters (I've seen this in other clues).
'bleak'+'loch'='bleakloch'
'bleakloch' with letters rearranged gives 'BLACK HOLE'.
(Other definitions for black hole that I've seen before include "Space left after collapse of a star" , "discovered in Calcutta" , "Astronomical curiosity" , "'Region of space from which nothing can escape (5,4)'" , "object in 21 [SPACE] having very strong 20 [GRAVITY]" .)