Transport Tom hired, right for a month in Paris once (9)
I believe the answer is:
thermidor
'a month in paris once' is the definition.
(month in the French Republican Calendar)
'transport tom hired right' is the wordplay.
'transport' indicates an anagram (letters are transported elsewhere).
'right' becomes 'r' (common abbreviation).
'tom'+'hired'='tomhired'
'tomhired' is an anagram of 'thermido'.
'thermido'+'r'='THERMIDOR'
'for' acts as a link.
(Other definitions for thermidor that I've seen before include "Method of cooking lobster" , "month of revolution" , "Revolutionary month (of the lobster?)" , "month in Paris once?" .)