One is spent travelling on foot
I believe the answer is:
instep
'foot' is the definition.
(thesaurus)
'one is spent travelling' is the wordplay.
'one' becomes 'i' (Roman numeral).
'travelling' indicates an anagram.
'spent' anagrammed gives 'nstep'.
'i'+'nstep'='INSTEP'
'on' is the link.
(Other definitions for instep that I've seen before include "Top of foot" , "Part of foot between toes and ankle" , "Arched part of foot" , "Part of foot/shoe" , "One part of Oxford" .)