Weaver caught in Peterloo massacre (4)
I believe the answer is:
loom
'weaver' is the definition.
(I've seen this before)
'caught in peterloo massacre' is the wordplay.
'caught in' indicates the answer is hidden within the clue.
'LOOM' can be found hidden inside 'peterloo massacre'.
(Other definitions for loom that I've seen before include "textile manufacturer" , "Textile machine; come into sight" , "Rise up threateningly ahead" , "Menace - weaving device" , "Appear large and indistinct, to weave?" .)