Less than acute, or referring to a disease or other abnormal condition which is present in a person who appears to be clinically well:

A subacute ailment may be identified or discovered with a laboratory test or radiologic examination.

The term subacute is used in contrast to "acute", which indicates "a very sudden onset or a rapid change", and "chronic" that indicates "an indefinite period of time or no change".

In ancient Greece, the "father of medicine", Hippocrates, distinguished diseases that were "acute" (abrupt, sharp and brief) from those that were "chronic" (sn illness or pain which is serious and that lasts for a long time). His diagnosis is still being applied in these modern times.

Subacute has been coined to designate the mid-ground between acute and chronic.