Lewis Short
(adj.adv.) : prōportĭōnālis, e, adj.proportio
* Of or belonging to proportion, proportional (post-class.): termini,Front. Colon. p. 111. —Hence, prōportĭōnālĭter, adv., proportionally, Cassiod. Geom. 6.
Charlton T. Lewis, Charles Short, A Latin Dictionary