Invalidate at the outset archaic names not used lately (5)
I believe the answer is:
annul
'invalidate' is the definition.
(I know that invalidate can be written as annul)
'at the outset archaic names not used lately' is the wordplay.
'at the outset' says to take the initial letters.
The first letters of 'archaic names not used lately' is 'ANNUL'.
(Other definitions for annul that I've seen before include "Cancel, abolish" , "Invalidate" , "Nullify" , "scratch" , "Cancel, revoke" .)