Send half a mile by taxi (5)
I believe the answer is:
cable
'send' is the definition.
(send a message by cable)
'half a mile by taxi' is the wordplay.
'half a' suggests halving the letters.
'by' is a charade indicator (letters next to each other).
'taxi' becomes 'cab' (synonyms).
'mile' cut in half is 'le'.
'le' put after 'cab' is 'CABLE'.
(Other definitions for cable that I've seen before include "Communication - wire - 200 yards in length" , "Telegram; thick rope" , "Hawser, wire" , "This may pull car up" , "Wire; message" .)