Useful, a.
Full of use, advantage, or profit; producing, or having power to produce, good; serviceable for any end or object; helpful toward advancing any purpose; beneficial; profitable; advantageous; as, vessels and instruments useful in a family; books useful for improvement; useful knowledge; useful arts. To what can I useful! Milton.
Shades of meaning
Fernald lists useful only as an antonym, under pernicious, vain.
He lists it without comment; the entries above explain its neighbors.
Synonyms
none given