Dance sexily at first with topless Serpent (5)
I believe the answer is:
samba
'dance' is the definition.
(Brazilian dance)
'sexily at first with topless serpent' is the wordplay.
'first' suggests taking the first letters.
'with topless serpent' becomes 'mba' (I am not sure about this - if you are sure you should believe this answer much more).
The first letters of 'sexily at' is 'sa'.
'sa'+'mba'='SAMBA'
Can you help me to learn more?
(Other definitions for samba that I've seen before include "Dance, originally from Brazil" , "Dance music" , "it was launched in Brazil" , "This ambassador's > brisk steps" , "Lively ballroom dance from Brazil" .)