One can, with energy, harangue traveller (9)
I believe the answer is:
itinerant
'traveller' is the definition.
(itinerant is a kind of traveller)
'one can with energy harangue' is the wordplay.
'one' becomes 'i' (Roman numeral).
'can' becomes 'tin' ('tin' can be a synonym of 'can').
'with' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mc2).
'harangue' becomes 'rant' ('rant' can be a synonym of 'harangue').
'i'+'tin'+'e'+'rant'='ITINERANT'
(Other definitions for itinerant that I've seen before include "Old labourer/traveller who travelled from place to place" , "Moving from place to place" , "Tie-in rant to a traveller" , "Nomad" , "Travelling from place to place" .)