Foster parent

A foster parent was one who acted as a caregiver, without legally adopting the child.

Bill Potts was brought up by her foster mother, Moira, after her birth mum died in Bill's infancy. (TV: The Pilot)

Matron Cofelia, of the Five-Straighten Classabindi Nursery Fleet, chose her human alias, "Miss Foster", as a reference to this role, as in fact she was fostering million of Adipose children. (TV: Partners in Crime)