Umbellar is an unusual word that refers to something that is related to an umbel or a flat-topped or rounded cluster of flowers. If you're looking for synonyms for this word, the first thing that comes to one's mind is "umbel-shaped," which means something is shaped like an umbel. Other synonyms for umbellar include "umbellate," "umbelled," and "umbelliform," each referring to things that have the same shape as an umbel. "Umbelliferous" refers to plants that bear umbels, while "umbellifer" is used to describe plants that belong to the family Umbelliferae or Apiaceae, which have flowers arranged in umbels.