Typical Royal Marines in Angola regularly left (6)
I believe the answer is:
normal
'typical' is the definition.
(similar in meaning)
'royal marines in angola regularly left' is the wordplay.
'royal marines' becomes 'RM' (abbreviation).
'in' is an insertion indicator.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'left' becomes 'l' (common abbreviation).
The alternating letters of 'angola' are 'noa'.
'rm' put into 'noa' is 'norma'.
'norma'+'l'='NORMAL'
(Other definitions for normal that I've seen before include "Standard; at right angles" , "Popular" , "Run-of-the-mill" , "Ordinary, usual" , "Average or ordinary" .)