At first, Sal’s pretty eyelashes cutely flutter (4)
I believe the answer is:
spec
'flutter' is the definition.
(flutter can mean a bet, type of speculation)
'at first sal's pretty eyelashes cutely' is the wordplay.
'at first' indicates taking the first letters.
The initial letters of 'sals pretty eyelashes cutely' is 'SPEC'.
(Other definitions for spec that I've seen before include "Required standard of workmanship" , "Requirement" , "Detailed design (colloq.)" , "on which chance is taken" , "Estimate" .)