What isn't multicellular?

Answer 1

Basically anything that not an aminal or plant, amond other things. Bacteria are probably the biggest group that comes to mind when talking about single cellularity, seeing as they do make up most of the biomass on earth. They are present in numbers of about 100 trillion in your body, while your body has something like 5-7 trillion human cells. Also though other single celled organisms are yeast, protozoans. But given the nature of your question far more things need to be included. Viruses are not considered living creatures, so they are not made of any cells at all, thus making them not multicellular. With that an eraser is not multicellular and neither is a bucket.