A handmaid, also known as a handmaiden, was a type of servant.
Katarina served as a handmaid to Cassandra. (TV: The Myth Makers [+]Donald Cotton, Doctor Who season 3 (BBC1, 1965).)
The Toymaker referred to Donna Noble and Melanie Bush as handmaidens when they stepped in to support the regenerating Fourteenth Doctor, each holding one of his hands. (TV: The Giggle [+]Russell T Davies, Doctor Who 2023 specials (BBC One and Disney+, 2023).)