Dance salsas and mambos — big ask, initially (5)
I believe the answer is:
samba
'dance' is the definition.
(sambaing is a kind of dancing)
'salsas and mambos big ask initially' is the wordplay.
'initially' says to take the initial letters.
The initial letters of 'salsas and mambos big ask' is 'SAMBA'.
(Other definitions for samba that I've seen before include "Brazilian dance" , "South American dance" , "Latin dance" , "it was launched in Brazil" , "Lively ballroom dance from Brazil" .)