Jack, on the road with Mac? (3)
I believe the answer is:
tar
'jack' is the definition.
(both are informal terms for sailor)
'the road with mac?' is the wordplay.
I cannot really see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is located in the answer.
The remaining letters 'ar' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'on' acts as a link.
Can you help me to learn more?
(Other definitions for tar that I've seen before include "Sailor and dressing for roads" , "Pitch; sailor" , "Art (anag.)" , "Slang sailor or road surfacing material" , "Dark viscous flammable substance" .)