Teasing adult I see in very old hat (7)
I believe the answer is:
archaic
'very old hat' is the definition.
(old hat means outdated or archaic)
'teasing adult i see' is the wordplay.
'teasing' becomes 'arch' (I've seen this in other clues).
'adult' becomes 'a' (abbreviation).
'see' becomes 'C' (the word for the letter, according to Chambers).
'arch'+'a'+'i'+'c'='ARCHAIC'
'in' acts as a link.
(Other definitions for archaic that I've seen before include "Extremely old" , "A long way out of date" , "Obsolete" , "No longer in general use" , "Antiquarian" .)