peekaboo

Short definition from Wiktionary

Noun

1. 1
   A game for a small child in which one covers one's face, then suddenly reveals it, saying "Boo!" or "Peekaboo!".

Adjective

1. 1
   With holes, slits or transparent fabric to reveal what is normally hidden.
2. 2
   Being or using a style of boxing with the hands kept close to the face to defend it.

Verb

1. 1
   To peep out.

Interjection

1. 1
   Boo (when showing oneself unexpectedly).