sitter

Etymology

From Middle English sitter, sittere, syttare, equivalent to sit + -er.

noun

1. Someone who sits, e.g. for a portrait.
   The photograph caused a stir last week because it was shortlisted for the National Portrait Gallery’s prestigious Taylor Wessing prize, despite the rule that “all photographs must have been taken by the entrant from life and with a living sitter”. However realistic Erica may be, and to me she looks more like a sex doll than a real person, she was certainly not a living sitter. September 10, 2017, Nigel Warburton, “What does a portrait of Erica the android tell us about being human?”, in The Observer
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. (soccer and snooker, slang) A very easy scoring chance.
   How could he miss that? It was an absolute sitter!
   Aaron Ramsey, a hero last season against Hull, missed a sitter at the end of normal time that would have made the game safe and must have been relieved that his shot against a post from four yards out did not cost his side more dearly. 18 April 2015, Paul Wilson, The Guardian