the.com/sitter

means A person who looks after someone else's child—or pet, or house—while they're away, usually for pay.

from Straightforward agent noun from 'sit' plus '-er': one who sits. The job-specific sense narrowed in through 'babysitter,' which emerged as a distinct term in the 20th century, then got clipped back down to just 'sitter' once context made the baby part obvious. 'House-sitter' and 'pet-sitter' followed the same pattern, borrowing the word's quiet, watchful logic—someone who occupies a space and minds what's in it, simply by staying put.