a person who is regarded as underhanded and furtive and contemptible
"The manager fired him after catching every employee sneaking into the office late at night to steal supplies."
someone acting as an informer or decoy for the police
"The suspect didn't know that his childhood friend was a sneak working undercover to gather evidence against him."
One who sneaks; one who moves stealthily to acquire an item or information.
"The thief acted as a sneak, slipping through the shadows to steal the jewels from the vault."
In plain English: A sneak is someone who acts dishonestly to get an advantage without anyone noticing.
"The thief hid his sneak in the back pocket until he left the store."
Usage: The noun form is often used informally to describe someone who enters a place secretly, but it can also refer specifically to a person who steals something by sneaking in. Avoid confusing this with the verb "sneak," which describes the action itself rather than the agent performing it.
To creep or go stealthily; to come or go while trying to avoid detection, as a person who does not wish to be seen.
"He managed to sneak out of the house through the back door just before his parents woke up."
In plain English: To sneak means to move quietly and secretly so that no one notices you are there.
"I slipped out of bed early to sneak past my brother without waking him up."
marked by quiet and caution and secrecy; taking pains to avoid being observed
"a furtive manner"
"a sneak attack"
"stealthy footsteps"
"a surreptitious glance at his watch"
In advance; before release to the general public.
"Fans managed to sneak a look at the unreleased movie trailer online."
In plain English: Sneaky describes someone who acts secretly to trick others or do something they shouldn't without getting caught.
"The sneaky mouse hid in the corner before we noticed him."
The word "sneak" likely comes from Old English snīcan, meaning "to creep or crawl." It traveled into modern usage with the same sense of moving quietly and furtively that its ancestor held centuries ago.