Very narrow lane, one running between hills (6)
I believe the answer is:
valley
'one running between hills' is the definition.
(I've seen this before)
'very narrow lane' is the wordplay.
'very' becomes 'v' (abbreviation).
'narrow lane' becomes 'alley' (I've seen this before).
'v'+'alley'='VALLEY'
(Other definitions for valley that I've seen before include "one depressed" , "Flat area of land flanked by hills" , "Low area between hills" , "Hollow between hills" , "Dale, dene or glen" .)