Start tailoring a new suit for the emperor (5)
I believe the answer is:
titus
'the emperor' is the definition.
(Roman emperor)
'start tailoring a new suit' is the wordplay.
'start' says to take the initial letters.
'a new' is an anagram indicator.
The initial letter of 'tailoring' is 't'.
'suit' with letters rearranged gives 'itus'.
't'+'itus'='TITUS'
'for' acts as a link.
(Other definitions for titus that I've seen before include "-- Groan, novel by Mervyn Peake" , "Roman emperor with arch" , "Only part of Shakespeare play" , "Roman emperor, son of Vespasian" , "Roman emperor from AD79" .)