Store not open to the public (5)
I believe the answer is:
stash
'store not' is the definition.
'stash' can be an answer for 'store' (I've seen this before). I'm not sure about the 'not' bit.
'open to the public' is the wordplay.
'open to' means one lot of letters goes inside another (some letters open up to include others).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'public' becomes 'sash' (I can't justify this - if you can you should believe this answer much more).
't' placed inside 'sash' is 'STASH'.
Can you help me to learn more?
(Other definitions for stash that I've seen before include "(Illegal) hoard" , "Secret(ly) store" , "Secret hoard" , "Hide (something) away" , "Squirrel away" .)