Sitter

noun

1. Someone who sits, e.g. for a portrait.
2. One employed to watch or tend something; a babysitter, housesitter, petsitter, etc.

   "It's always such a pain to get a sitter on short notice."

3. A participant in a séance.
4. A broody hen.
5. A very easy scoring chance.

   "How could he miss that? It was an absolute sitter!"