Reversing small car I call almost pernicious (8)
I believe the answer is:
inimical
'pernicious' is the definition.
(I've seen this before)
'reversing small car i call almost' is the wordplay.
'reversing' says the letters should be written in reverse.
'small car' becomes 'mini' (I've seen this before).
'almost' means to remove the last letter (most of the word but not all of it).
'mini' back-to-front is 'inim'.
'call' with its last letter removed is 'cal'.
'inim'+'i'+'cal'='INIMICAL'
(Other definitions for inimical that I've seen before include "Adverse" , "'Unfriendly, hostile (8)'" , "Hostile, antagonistic" , "Hostile, unfavourable" , "Hostile or in opposition" .)