"Sneak"can be a verb (v), noun(n), or adjective(adj), For ex. (v) = Sneak a look. (secretly looking) (n) = A sneak was caught in accident. (A spy was caught. A person sneaking was caught); (adj)= A sneak movement. (An unnoticed actions) To make this simple. Whatever secretly you're doing it's a sneak. You will also hear this word for movies like "sneak preview" this means that you are looking at it secretly in partial of the whole, or just a glance.

Sneak 1- to go somewhere secretly, trying to avoid being seen Sneak = creep: I sneaked up the stairs. 2 - to do sth or take sb/sth somewhere secretly, often without permission: [vn] We sneaked a look at her diary. I managed to sneak a note to him. I managed to sneak him a note.

PHRASAL VERBS sneak 'up (on sb/sth) to move towards sb very quietly so that they do not see or hear you until you reach them: He sneaked up on his sister and shouted ‘Boo!’. noun(old-fashioned, BrE, disapproving) a person, especially a child, who tells sb about sth wrong that another person has done Sneak = snitch adjective[only before noun] done without any warning: a sneak attack

3- (informal) to secretly take sth small or unimportant Sneak = pinch: I sneaked a cake when they were out of the room. 4- sneak (on sb) (to sb) (old-fashioned, BrE, disapproving) to tell an adult that another child has done sth wrong, especially in order to cause trouble Sneak = snitch: Did you sneak on me to the teacher?