They had a platonic friendship, not a romantic one.
Our relationship was strictly platonic.
Whereas in the more northerly clime of England the courtly lover of Malory and the Round Table tended to platonic adoration from afar, the Parisian woman already expected—and received—more earthly devotion. —Alistair Horne, Seven Ages of Paris, 2002
Relax. The Three Phils are strictly platonic. Yet three-pal business relationships are just as vulnerable to messy implosions as their romantic counterparts. —Anne Marie Cruz, ESPN, 7 Feb. 2000
… before concluding that your PC is for work and not pleasure, try hooking up a couple of first-rate speakers and then planting yourself in the platonic ideal of the chair. —Fortune, Summer 1998