noun, noun or participle which takes 'suru'
nursing a patient; caring for the sick
Rare and somewhat old-fashioned; modern Japanese typically uses 看病 (かんびょう) instead. May still appear in literary or historical contexts.
彼女は夜通し母の介病をした。
She nursed her mother all night.
看病 is the common modern word for nursing a patient. 介病 is rare and may sound archaic or literary.
The exact derivation is uncertain; the kanji 介 (mediate, help) and 病 (illness) suggest 'assisting with illness'.