Meaning of SITTER in English
1》 a person who sits, especially for a portrait or examination.
↘a sitting hen.
2》 [usu. in combination ] a person who looks after children, pets, or a house while the parents or owners are out or away: a house-~.
↘a person who provides care and companionship for people who are ill.
3》 Brit. informal (in sport) an easy catch or shot.
Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004