War cry from that corps regularly (5)
I believe the answer is:
whoop
'war cry' is the definition.
(I've seen this before)
'that corps regularly' is the wordplay.
'that' becomes 'who' (the person that..., the person who...).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'corps' are 'op'.
'who'+'op'='WHOOP'
'from' is the link.
(Other definitions for whoop that I've seen before include "Joyful shout" , "Sound of war cry (or cough!)" , "Shout, as if with joy or enthusiasm" , "Loud excited cry" , "Loud cry of triumph" .)