Worry about large old piece of broccoli (6)
I believe the answer is:
floret
'piece of broccoli' is the definition.
(I've seen this before)
'worry about large old' is the wordplay.
'worry' becomes 'fret' (fretting is a kind of worrying**).
'about' indicates putting letters inside.
'large' becomes 'l'.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'l'+'o'='lo'
'fret' placed around 'lo' is 'FLORET'.
(Other definitions for floret that I've seen before include "Part of cauli head" , "Part of a cauliflower or broccoli head" , "Broccoli stem" , "Small flower" , "Piece of broccoli" .)