Lied about extremities of tower being robust? (6)
I believe the answer is:
strong
'robust?' is the definition.
('strong' can be similar in meaning to 'robust')
'lied about extremities of tower' is the wordplay.
'lied' becomes 'song' ('Lied' is German for song).
'about' is an insertion indicator.
'extremities of' suggests removing the centre.
'tower' with its centre taken out is 'tr'.
'song' enclosing 'tr' is 'STRONG'.
'being' acts as a link.
(Other definitions for strong that I've seen before include "is excelling" , "Robust and muscular" , "Mighty, powerful" , "Great in power" , "Convincing" .)