One more flower part, organ originally inside (7)
I believe the answer is:
another
'one more' is the definition.
(I've seen this before)
'flower part organ originally inside' is the wordplay.
'flower part' becomes 'anther' ('anther' is part of 'flower').
'originally' suggests taking the first letters.
'inside' means one lot of letters goes inside another.
The first letter of 'organ' is 'o'.
'anther' placed around 'o' is 'ANOTHER'.
(Other definitions for another that I've seen before include "Additional: alternative" , "A different (thing)" , "Someone else" , "A different one" , "Player or person not yet named or selected" .)