One adult after posh cap finds ideal place (6)
I believe the answer is:
utopia
'ideal place' is the definition.
(I've seen this before)
'one adult after posh cap' is the wordplay.
'one' becomes 'i' (Roman numeral).
'adult' becomes 'a'.
'after' means one lot of letters go next to another.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'cap' becomes 'top' ('top' can be a synonym of 'cap').
'i'+'a'='ia'
'u'+'top'='utop'
'ia' after 'utop' is 'UTOPIA'.
'finds' is the link.
(Other definitions for utopia that I've seen before include "Heaven" , "place of bliss" , "Literally nowhere" , "Supposed ideal land" , "Thomas More's favourite place" .)