Platonic love is an affectionate relationship into which the sexual element does not enter, especially in cases where one might easily assume otherwise. The English term dates back as far as Sir William Davenant's Platonic Lovers (1636). It is derived from the concept in Plato's Symposium, of the love of the idea of good which lies at the root of all virtue and truth.
The term amor platonicus was used as early as the 15th Century by Marsilio Ficino, as a synonym for "amor socraticus," referring to the affection between Socrates and his pupils. This article incorporates text from the public domain 1911 Encyclopædia Britannica.
"Platonic Love is a fool's name for the affection between a disability and a frost." - Ambrose Bierce