Source : Webster's Revised Unabridged Dictionary (1913)

Useful \Use"ful\, 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.

Source : WordNet®

useful
     adj 1: being of use or service; "the girl felt motherly and
            useful"; "a useful job"; "a useful member of society"
            [syn: {utile}] [ant: {useless}]
     2: of great importance or use or service; "useful information";
        "valuable advice" [syn: {valuable}, {of value}]
     3: capable of being turned to use or account; "useful
        applications of calculus"
     4: having a useful function; "utilitarian steel tables" [syn: {utilitarian}]