the GNU version of the Collaborative International Dictionary of English
n. One who encourages, incites, or helps forward; a favorer.
The Century Dictionary and Cyclopedia
n. One who encourages, incites, or stimulates to action; one who promotes or advances.
Word Usage
"Ackerman's own contribution to SF fiction was reasonable - over fifty short stories and novels, some of them published under pseudonyms or in collaboration - but as an editor and 'encourager' his role was more pronounced."