Stays for altering a waist! (6)
I believe the answer is:
awaits
'stays' is the definition.
Although both the answer and definition are verbs in their -s form, I cannot understand how one could define the other.
'altering a waist' is the wordplay.
'altering' indicates anagramming the letters.
'a'+'waist'='awaist'
'awaist' with letters rearranged gives 'AWAITS'.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for awaits that I've seen before include "Looks forward to" , "Looks for; is in store for" , "Doesn't go" , "Expects" .)