Abbreviation of post post post script.

Third-person singular simple present indicative form of involute

Designating the 1232 work of ethics, Akhlaq-i Nāṣirī (Nasirean Ethics), by the Persian polymath Naṣīr al-Dīn al-Ṭūsī (1201–1274).

(chiefly physics) Tending toward the center or axis