Thus there is hesitation to travel (4)
I believe the answer is:
ergo
'thus' is the definition.
(thesaurus)
'hesitation to travel' is the wordplay.
'hesitation' becomes 'er'.
'to travel' becomes 'go' ('go' can be a synonym of 'travel').
'er'+'go'='ERGO'
'there is' is the link.
(Other definitions for ergo that I've seen before include "for this reason" , "Therefore - what a goer" , "as a consequence" , "Therefore (Latin)" , "so philosopher wrote in Latin" .)