Humorous article, on reflection (7)
I believe the answer is:
amusing
'humorous' is the definition.
(I've seen this before)
'article on reflection' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'reflection' becomes 'musing' (synonyms).
'a'+'musing'='AMUSING'
(Other definitions for amusing that I've seen before include "Pleasantly entertaining" , "comic" , "Mildly funny - diverting" , "Droll" , "Pleasantly diverting" .)