(something)-to-be
Used in a compound with a noun to indicate what someone something will become in the near future. The weekly seminar is aimed at giving mothers-to-be some practical information about childbirth and the early days thereafter. You should come down for the weekend sometime soon! We'd love to meet your husband-to-be.
-to-be
of the future. 1993 Mother & Baby Many mums-to-be report that small frequent snacks are easier to keep down than three large meals a day.
-to-be
(in compounds) future: his bride-to-bemothers-to-be (= pregnant women)