One evenly burns in the ads (6)
I believe the answer is:
united
'one' is the definition.
('united' can be a synonym of 'one')
'evenly burns in the ads' is the wordplay.
'evenly' indicates alternate letters (even-numbered letters only).
'burns'+'in'+'the'+'ads'='burnsintheads'
The alternating letters of 'burnsintheads' are 'UNITED'.
(Other definitions for united that I've seen before include "Joined in marriage" , "Amalgamated" , "In agreement" , "what may be seen after Oxford and Cambridge?" , "Merged into one" .)