(1) A virtual X (where X is a common noun) is something, not an X, which has the efficiency (virtus) of an X.
This is the proper meaning of the word; but (2) it has been seriously confounded with ‘potential,’ which is almost its contrary. For the potential X is of the nature of X, but is without actual efficiency. A virtual velocity is something not a velocity, but a displacement; but equivalent to a velocity in the formula, ‘what is gained in velocity is lost in power.’
So virtual representation was the non-representation of the American colonies in the British Parliament, which was supposed to be replaced by something. So Milton asks whether the angels have virtual or immediate touch. So, too, the sun was said to be virtualiter on earth, that is, in its efficiency.
(3) Virtual is sometimes used to mean pertaining to virtue in the sense of an ethical habit.
…a “virtual x,” where x stands for a common noun, means something which is not an x, but which has, for whatever purpose may be uppermost, the virtue of an x, that is, such properties as make it equivalent to an x.
“Virtual,” followed by any common noun, say ‘N,’ makes an appellative phrase which denotes anything which, while it is not an ‘N,’ has, nevertheless, the characteristic behaviour and properties of an ‘N.’