Assistant, n.
1. One who, or that which, assists; a helper; an auxiliary; a means of help. Four assistants who his labor share. Pope. Rhymes merely as assistants to memory. Mrs. Chapone.
2. An attendant; one who is present. Dryden.
1 other Webster entry under this spelling
Assistant, a.
1. Helping; lending aid or support; auxiliary. Genius and learning . . . are mutually and greatly assistant to each other. Beattie.
2. (Mil.)
Of the second grade in the staff of the army; as, an assistant surgeon. [U.S.]
Note: In the English army it designates the third grade in any particular branch of the staff. Farrow.
Shades of meaning
Fernald has no entry of its own for assistant; he lists it under accessory, auxiliary.
Where he writes about it:
Colleague is used always in a good sense, associate and coadjutor generally so; ally, assistant, associate, attendant, companion, helper, either in a good or a bad sense; abetter, accessory, accomplice, confederate, almost always in a bad sense. — from accessory
A surgeon's assistant is a physician or medical student who shares in the treatment and care of patients; a surgeon's attendant is one who rolls bandages and the like. — from accessory
Yet the auxiliary is more than a mere assistant. — from auxiliary