mound builder is a noun meaning "prehistoric Amerindians who built altar mounds". It carries 2 recorded senses.
prehistoric Amerindians who built altar mounds
large-footed short-winged birds of Australasia; build mounds of decaying vegetation to incubate eggs
Definitions, synonyms and semantic relations for mound builder come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.