Shape of unloaded trailer, one thrown into fire (8)
I believe the answer is:
triangle
'shape' is the definition.
(triangle is a kind of shape)
'unloaded trailer one thrown into fire' is the wordplay.
'unloaded' suggests removing the centre (the content of the word is unloaded).
'one' becomes 'a'.
'thrown into' is an insertion indicator.
'fire' becomes 'ingle' (I've seen this before).
'trailer' with its middle taken out is 'tr'.
'a' placed into 'ingle' is 'iangle'.
'tr'+'iangle'='TRIANGLE'
'of' is the link.
(Other definitions for triangle that I've seen before include "kitchen item" , "Alerting (anag)" , "Three-sided shape" , "Regular shape with" , "Constellation - three-sided figure" .)