Emperor initially tickled by new suit (5)
I believe the answer is:
titus
'emperor' is the definition.
(Roman emperor)
'initially tickled by new suit' is the wordplay.
'initially' suggests taking the first letters.
'by' means one lot of letters go next to another.
'new' indicates anagramming the letters.
The initial letter of 'tickled' is 't'.
'suit' with letters rearranged gives 'itus'.
't'+'itus'='TITUS'
(Other definitions for titus that I've seen before include "& 20 Mervyn Peake character" , "recipient of holy letter" , "good book" , "Groan, possibly" , "Roman emperor - one of St Paul's correspondents" .)