Flowers happy one fed with exotic oil (8)
I believe the answer is:
gladioli
'flowers' is the definition.
(I've seen this before)
'happy one fed with exotic oil' is the wordplay.
'happy' becomes 'glad' (similar in meaning).
'one' becomes 'I' (Roman numeral).
'fed with' indicates putting letters inside.
'exotic' indicates anagramming the letters.
'glad'+'i'='gladi'
'oil' is an anagram of 'iol'.
'gladi' placed around 'iol' is 'GLADIOLI'.
(Other definitions for gladioli that I've seen before include "Flowers in spikes (starting happy)" , "I laid log in the flowers" , "Did the Iliad log out these flowers?" , "Tall garden flowers" , "Plant with brightly coloured, funnel-shaped flowers" .)