Peal of thunder restricts flying (5)
I believe the answer is:
aloft
'flying' is the definition.
(I've seen this in another clue)
'peal of thunder restricts' is the wordplay.
'restricts' indicates the answer is hidden within the clue (the answer is held or restricted by the clue).
'ALOFT' is hidden within 'peal of thunder'.
(Other definitions for aloft that I've seen before include "Above - on top" , "At a considerable height" , "Up in the sky" , "Skyward" , "in a high position" .)