simple substance; elementary substance
Chemistry term: a substance consisting of atoms of a single element, as opposed to a compound.
Oxygen exists as a simple substance.
This lens can also be used on its own.
standalone; separate item; solo item
General use: something that is alone, not part of a set or combination; often used in contrast to compound or combined items.
This part is also sold separately.
It's weak on its own, but powerful when combined.
You can purchase the battery separately.
単体 refers to a substance made of a single element, while 化合物 is a compound formed from multiple elements bonded together.
単体 means a standalone item or elementary substance, while 単一 means simple or uniform, focusing on homogeneity rather than being separate.
From 単 (simple, single) + 体 (body, substance). The chemistry sense is a direct translation of the Western concept of 'simple substance'.