HUMOUR, from the Latin humor, in its original signification, stands for moisture in general; from whence it has been restrained to signify the moisture of animal bodies, or those fluids which circulate through them.
It is distinguished from moisture in general in this, that humours properly express the fluids of the body; when in a vitiated state, it would not be improper to say, that the fluids of such a person's body were full of humours.
The only fluids of the body, which, in their natural and healthful state, are called humours, are those in the eye; we talk of the aqueous humour, the crystalline humour, without meaning any thing that is morbid or diseased: yet when we say in general, that such a person has got a humour in his eye, we understand it in the usual sense of a vitiated fluid.
As the temper of the mind is supposed to depend upon the state of the fluids in the body, humour has come to be synonymous with temper and disposition. A person's humour, however, is different from his disposition; in this, that humour seems to be the disease of a disposition: it would be proper to say that persons of a serious temper or disposition of mind, were subject to melancholy humours; that those of a delicate and tender disposition, were subject to peevish humours.
Humour may be agreeable or disagreeable: but it is still humour; something that is whimsical, capricious, and not to be depended upon. An ill-natured man may have fits of good-humour, which seem to come upon him accidentally, without any regard to the common moral causes of happiness or misery.
A fit of cheerfulness constitutes the whole of good-humour; and a man who has many such fits, is a good-humoured man: yet he may not be good-natured; which is a character that supposes something more constant, equable, and uniform, than what is requisite to constitute good humour.