Nominal half-mile in a taxi (5)
I believe the answer is:
Here is my best explanation:
'nominal' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'half-mile in a taxi' is the wordplay.
'half' suggests halving the letters.
'in' means one lot of letters goes inside another.
'a taxi' becomes 'cab' (synonyms).
'mile' with half the letters taken is 'le'.
'le' going into 'cab' is 'CALEB'.