It is multi celled.
Single
Single-cell
Bacteria are single-celled organisms
multi celled
They are multi-cellular.
multi celled of coures
multi celled
Onions are multicellular, but this term refers to the entire organism - you cannot call a single onion cell a "multi cell".
a slime mold
Turtles are definitely multi-celled. Single cell organisms are microorganisms such as bacteria and the protozoans.
Fungi can be both single-celled (yeast) or multicellular (mushrooms).