Collect a million as head of security (5)
I believe the answer is:
amass
'collect' is the definition.
('amass' can be a synonym of 'collect')
'a million as head of security' is the wordplay.
'million' becomes 'm' (abbreviation).
'head of' indicates taking the first letters.
The first letter of 'security' is 's'.
'a'+'m'+'as'+'s'='AMASS'
(Other definitions for amass that I've seen before include "Build up" , "Accumulate, pile up" , "Get together" , "Be a compiler" , "Collect, hoard" .)