The Collaborative International Dictionary of English v.0.48:
Foster \Fos"ter\, a. [AS. f[=o]ster, f[=o]stor, nourishment. See
Foster, v. t.]
Relating to nourishment; affording, receiving, or sharing
nourishment or nurture; -- applied to father, mother, child,
brother, etc., to indicate that the person so called stands
in the relation of parent, child, brother, etc., as regards
sustenance and nurture, but not by tie of blood.
Foster babe or Foster child, an infant or child nursed or
raised by a woman not its mother, or bred by a man not its
Foster brother, Foster sister, one who is, or has been,
nursed at the same breast, or brought up by the same nurse
as another, but is not of the same parentage.
Foster dam, one who takes the place of a mother; a nurse.
Foster earth, earth by which a plant is nourished, though
not its native soil. --J. Philips.
Foster father, a man who takes the place of a father in
caring for a child. --Bacon.
(a) Land allotted for the maintenance of any one. [Obs.]
(b) One's adopted country.
Foster lean [foster + AS. l[ae]n a loan See Loan.],
remuneration fixed for the rearing of a foster child;
also, the jointure of a wife. [Obs.] --Wharton.
Foster mother, a woman who takes a mother's place in the
nurture and care of a child; a nurse.
Foster nurse, a nurse; a nourisher. [R.] --Shak.
Foster parent, a foster mother or foster father.
Foster son, a male foster child.