Gasp about large factory (5)
I believe the answer is:
plant
'factory' is the definition.
(a manufacturing plant)
'gasp about large' is the wordplay.
'gasp' becomes 'pant' (synonyms).
'about' is an insertion indicator.
'large' becomes 'L' (eg in clothes sizes).
'pant' enclosing 'l' is 'PLANT'.
(Other definitions for plant that I've seen before include "Machinery; spy" , "that goes to pot" , "Factory equipment" , "eg Flower" , "Put in soil" .)