Fits up local possibly sold out by the opticians (6)
I believe the answer is:
frames
This clue could be a double definition.
'fits up local possibly sold out' is the first definition.
The answer and definition can be both to do with fundamental existence as well as being verbs in their -s form.
Perhaps they are linked in a way I don't understand?
'the opticians' is the second definition.
Although both the answer and definition are plural nouns, I don't understand how one could define the other.
'by' acts as a link.
Can you help me to learn more?
(Other definitions for frames that I've seen before include "Borders, around pictures say" , "Rounds of snooker play, or spectacles structures" , "Supporting or surrounding structures" .)