In context|botany|lang=en terms the difference between flower and hypanthium

is that flower is (botany) a reproductive structure in angiosperms (flowering plants), often conspicuously colourful and typically including sepals, petals, and either or both stamens and/or a pistil while hypanthium is (botany) the bowl-shaped part of a flower on which the sepals, petals, and stamens are borne.

As nouns the difference between flower and hypanthium

is that flower is a colorful, conspicuous structure associated with angiosperms, frequently scented and attracting various insects, and which may or may not be used for sexual reproduction or flower can be something that flows, such as a river while hypanthium is (botany) the bowl-shaped part of a flower on which the sepals, petals, and stamens are borne.

As a verb flower

is to put forth blooms.