Bitterly cold truck transporting ice essentially (6)
I believe the answer is:
arctic
'bitterly cold' is the definition.
(I've seen this in another clue)
'truck transporting ice essentially' is the wordplay.
'truck' becomes 'artic' (short for articulated lorry).
'transporting' is an insertion indicator.
'essentially' means to look at the middle letters.
The middle of 'ice' is 'c'.
'artic' going around 'c' is 'ARCTIC'.
(Other definitions for arctic that I've seen before include "Bitter" , "Cold region in the northern hemisphere" , "Area around the North Pole" , "perishing" , "Very cold as in the far north" .)