To people, one is a danger (6)
I believe the answer is:
menace
'danger' is the definition.
(I know that menace is a type of danger)
'to people one' is the wordplay.
'to people' becomes 'men' (men are people).
'one' becomes 'ace' (ace has a value of one in some card games).
'men'+'ace'='MENACE'
'is a' is the link.
(Other definitions for menace that I've seen before include "Serious threat" , "Act in a threatening manner" , "A threatening quality" , "Intimidate" , "A source of danger" .)