Synaesthesia

M. [Théodore] Flournoy includes all the phenomena of "Colored Hearing" and of "Mental Forms" under the convenient and adequate name Synæsthesia—in place of which, to be sure, he himself usually employs the less defensible term Synopsie. […] The phenomena of synæsthesia are divided into three main groups: "photisms," among which are included, as by [Eugen] Bleuler and Lehmann, all the varieties of pseudo-chromesthesia; "Schemes," comprising not only "forms" (diagrammes) associated with series of words or numbers, but "symbols," or particular figures associated with single letters, numerals, colors and the like; and "personifications," in which the associated factor is no mere color or form, but has become richer and more concrete.

Source: wiktionary

Probably in all of us, though in some men much more distinctly than in others, there exist certain synæsthesiæ or concomitances of sense-impression, which are at any rate not dependent on any recognisable link of association.

Source: wiktionary

[…] R. H. Gault's case of synesthesia in a deaf and blind girl, who could distinguish colors by the sense of smell, […]

Source: wiktionary

Now just as normal perceptions in terms of sense organs different from those stimulated can be interpreted through common past experiences, so it is likely that synæsthesias may be partly explicable in terms of individual experiences.

Source: wiktionary