Threaten people with card (6)
I believe the answer is:
menace
'threaten' is the definition.
(I know that threaten can be written as menace)
'people with card' is the wordplay.
'people' becomes 'men' (men are people).
'with' says to put letters next to each other.
'card' becomes 'ace' (ace is a type of playing card).
'men'+'ace'='MENACE'
(Other definitions for menace that I've seen before include "Intimidation" , "ominous atmosphere" , "Act in a threatening manner" , "Threat; threaten" , "A source of danger" .)