Park always admitting one radio (8)
I believe the answer is:
receiver
'radio' is the definition.
(thesaurus)
'park always admitting one' is the wordplay.
'park' becomes 'rec' (I've seen this in other clues).
'always' becomes 'ever' ('ever' can be a synonym of 'always').
'admitting' is an insertion indicator.
'one' becomes 'i' (Roman numeral).
'ever' going around 'i' is 'eiver'.
'rec'+'eiver'='RECEIVER'
(Other definitions for receiver that I've seen before include "Equipment to take radio or tv signals" , "Official who administers property under court order" , "Beneficiary; fence" , "Person dealing with property of bankrupt" , "Criminal illegally handling" .)