The Commens Dictionary
Quote from ‘The Basis of Pragmaticism’
A sign is plainly a species of medium of communication, and medium of communication is a species of medium, and a medium is a species of third. [—]
A medium of communication is something, A, which being acted upon by something else, N, in its turn acts upon something, I, in a manner involving its determination by N, so that I shall thereby, through A and only through A, be acted upon by N.