provitamin A

Any of the carotenoids that are precursors of vitamin A and exhibit qualitatively the biological activity of beta-carotene; they are present in fish-liver oils, egg yolk, milk products, and green-leaf or yellow vegetables and fruits.

The noun has one meaning:

Meaning #1: an orange isomer of an unsaturated hydrocarbon found in many plants; is converted into vitamin A in the liver
  Synonyms: carotene, carotin