noun, used as a suffix, noun
Used as a suffix in medical or descriptive terms for specific types of pain (e.g., 頭痛, 腹痛), and occasionally as a standalone noun meaning 'pain' or 'ache'.
頭痛がひどいので、薬を飲んだ。
I had a bad headache, so I took medicine.
腹痛の原因はまだわからない。
The cause of the stomachache is still unknown.
痛み is the common native Japanese word for 'pain', used in everyday language. 痛 is more technical and often appears as a suffix in compound medical terms.
The kanji 痛 is used in Sino-Japanese compounds to express pain. The reading つう is the on'yomi, commonly used in medical terminology.