Adjunct, a.
Etymology: [L. adjunctus, p. p. of adjungere. See Adjoin.]
Conjoined; attending; consequent. Though that my death were adjunct to my act. Shak. Adjunct notes (Mus.), short notes between those essential to the harmony; auxiliary notes; passing notes.
1 other Webster entry under this spelling
Adjunct, n.
1. Something joined or added to another thing, but not essentially a part of it. Learning is but an adjunct to our self. Shak.
2. A person joined to another in some duty or service; a colleague; an associate. Wotton.
3. (Gram.)
A word or words added to quality or amplify the force of other words; as, the History of the American Revolution, where the words in italics are the adjunct or adjuncts of "History."
4. (Metaph.)
A quality or property of the body or the mind, whether natural or acquired; as, color, in the body, judgment in the mind.
5. (Mus.)
A key or scale closely related to another as principal; a relative or attendant key. [R.] See Attendant keys, under Attendant, a.
Shades of meaning
Fernald has no entry of its own for adjunct; he lists it under appendage.
Where he writes about it:
An adjunct (something joined to) constitutes no real part of the thing or system to which it is joined, tho perhaps a valuable addition; an appendage is commonly a real, tho not an essential or necessary part of that with which it is connected; an appurtenance belongs subordinately to something by which it is employed, especially as an instrument to accomplish some purpose. — from appendage
A horse's tail is at once an ornamental appendage and a useful appurtenance; we could not call it an adjunct, tho we might use that word of his iron shoes. — from appendage