idle/empty threat

: lacking worth or basis : vain

: not occupied or employed: such as

: having no employment : inactive

: to spend time in idleness

: to move idly

: to run at low power and often disconnected usually so that power is not used for useful work

: containing nothing

: not occupied or inhabited

: unfrequented

: to make empty : remove the contents of

: deprive, divest

: to discharge (itself) of contents

: something (such as a bottle or can) that is empty

: an expression of intention to inflict evil, injury, or damage

: one that threatens

: an indication of something impending

: threaten