Thinner lassies talk about the rest (6)
I believe the answer is:
siesta
'the rest' is the definition.
(I've seen this before)
'thinner lassies talk about' is the wordplay.
'about' says the answer is hidden in the clue (the clue goes around or about the answer).
'SIESTA' can be found hidden inside 'thinner lassies talk'.
(Other definitions for siesta that I've seen before include "Afternoon nap in Cadiz" , "Catnap" , "Rest in the heat of the day" , "Afternoon nap in a warm climate" , "PM snooze" .)