One's stay on motorway in the same place (6)
I believe the answer is:
ibidem
'in the same place' is the definition.
('ibidem' can be a synonym of 'in the same place')
'one's stay on motorway' is the wordplay.
'one' becomes 'i' (Roman numeral).
'stay on' becomes 'bide' (biding is a kind of staying on).
'motorway' becomes 'm'.
'i'+'bide'+'m'='IBIDEM'
(Other definitions for ibidem that I've seen before include "In the same source (Latin)" , "In the same place as previous reference" , "In the same place, used in referencing" , "Notation meaning in same book or passage, often shortened" , "In reference notes, denotes in the same place" .)