Understand article and be very angry (6)
I believe the answer is:
seethe
'be very angry' is the definition.
(I've seen this before)
'understand article' is the wordplay.
'understand' becomes 'see' (synonyms).
'article' becomes 'the' (the definite article in English).
'see'+'the'='SEETHE'
'and' acts as a link.
(Other definitions for seethe that I've seen before include "Boil, be turbulent" , "Be filled with intense but unexpressed anger" , "Be furious" , "Feel intense rage" , "Ferment, sizzle" .)