Corps put faith in security (4,5)
I believe the answer is:
unit trust
'security' is the definition.
(financial term)
'corps put faith' is the wordplay.
'corps' becomes 'unit' (a unit is a corps in the army).
'put' says to put letters next to each other.
'faith' becomes 'trust' (synonyms).
'unit'+'trust'='UNIT TRUST'
'in' is the link.
(Other definitions for unit trust that I've seen before include "Investment fund" , "Form of investment" , "Investment system" , "Investment package" , "Multiple investment scheme" .)