Shrub in old list of French rarities, principally (8)
I believe the answer is:
oleander
'shrub' is the definition.
(I've seen this before)
'old list of french rarities principally' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'list' becomes 'lean' (both can mean to tilt).
'of french' becomes 'de' ('of' in French).
'principally' suggests taking the first letters.
The first letter of 'rarities' is 'r'.
'o'+'lean'+'de'+'r'='OLEANDER'
'in' acts as a link.
(Other definitions for oleander that I've seen before include "Reloaned for evergreen shrub with bright flowers" , "Flowering plant" , "bloomer" , "Poisonous evergreen shrub with white, pink or red flowers" , "Mediterranean shrub" .)