Synonyms for By-blow:

n.

by-blow (noun)
whoreson, love child, illegitimate, illegitimate child.
illegitimate child (noun)
whoreson, love child.
love child (noun)
illegitimate child.
person (noun)
whoreson, love child, illegitimate, illegitimate child.

Other synonyms:

n.
love child, illegitimate child.