Regularly goes by Pentagon stratagem (5)
I believe the answer is:
dodge
'stratagem' is the definition.
('dodge' can be a synonym of 'stratagem')
'regularly goes by pentagon' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'by' is a charade indicator (letters next to each other).
'pentagon' becomes 'dod' (US Department of Defense, based in the Pentagon).
The alternate letters of 'goes' are 'ge'.
'ge' after 'dod' is 'DODGE'.
(Other definitions for dodge that I've seen before include "Avoid by sudden movement" , "Wheeze" , "Evade - sidestep" , "Avoid or attempt to" , "Evade by moving out of the way" .)