Apologetic with small truck not starting (5)
I believe the answer is:
sorry
'apologetic' is the definition.
(I've seen this before)
'small truck not starting' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'truck' becomes 'lorry' (lorry is a kind of truck).
'not starting' means to remove the first letter.
'lorry' with its first letter removed is 'orry'.
's'+'orry'='SORRY'
'with' acts as a link.
(Other definitions for sorry that I've seen before include "Penitent; regrettable" , "Regretful, apologetic" , "In a pitiful state; apologetic" , "Feeling penitence" , "I didn't quite catch that?" .)