Crown I found inside O'Hara's plantation (5)
I believe the answer is:
tiara
'crown' is the definition.
(thesaurus)
'i found inside o'hara's plantation' is the wordplay.
'found inside' means one lot of letters goes inside another.
'o'hara's plantation' becomes 'tara' (ref to Scarlett O'Hara from Gone with the Wind).
'i' inserted within 'tara' is 'TIARA'.
(Other definitions for tiara that I've seen before include "expensive headwear" , "Jewelled headwear" , "Pope's triple-tiered crown" , "Woman's headdress for very formal occasions" , "Ornamental headpiece" .)