Article about an old clan chief, Macbeth, for example (5)
I believe the answer is:
thane
'old clan chief macbeth for example' is the definition.
(Shakespeare's Macbeth was Thane of Glamis)
'article about an' is the wordplay.
'article' becomes 'the' (the definite article in English).
'about' means one lot of letters goes inside another.
'the' enclosing 'an' is 'THANE'.
(Other definitions for thane that I've seen before include "Macbeth's Cawdor title" , "Anglo-Saxon noble of lower rank" , "Anglo-Saxon king's companion; neath (anag.)" , "Macbeth was made -- of Cawdor" , "Medieval Scottish clan chief" .)