Periodical trouble working back in bush (8)
I believe the answer is:
magnolia
'bush' is the definition.
(I know that Magnolia is a bush)
'periodical trouble working back' is the wordplay.
'periodical' becomes 'mag' (abbreviation for magazine).
'trouble' becomes 'ail' (synonyms).
'working' becomes 'on' (on can mean working or activated).
'back' shows that the letters should be reversed in order.
'ail'+'on'='ailon'
'ailon' back-to-front is 'nolia'.
'mag'+'nolia'='MAGNOLIA'
'in' acts as a link.
(Other definitions for magnolia that I've seen before include "Tree with showy flowers" , "Fragrant bloom might strangely gain loam" , "Spring-flowering tree" , "Mississippi, the ___ State - tree or shrub" , "Creamy white, shrub" .)