In botany terms the difference between flower and synanthy

is that flower is 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 synanthy is the abnormal fusion of two or more flowers.

As nouns the difference between flower and synanthy

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 while synanthy is the abnormal fusion of two or more flowers.

As a verb flower

is to put forth blooms.