Train coming from southern part of Hertfordshire (6)
I believe the answer is:
string
'train' is the definition.
(I know that train can be written as string)
'southern part of hertfordshire' is the wordplay.
I cannot really see how this works, but
'southern' could be 's' (abbreviation) and 's' is found in the answer.
'part' could be 'in' (synonyms) and 'in' is located in the answer.
This explanation may well be incorrect...
'coming from' is the link.
Can you help me to learn more?
(Other definitions for string that I've seen before include "Length of narrow cord" , "Number of racehorses" , "Violin wire/catgut" , "tier" , "Thread; sequence" .)