English Noun founder member (plural founder members) (UK) Synonym of founding member Further reading “founder member”, in Cambridge English Dictionary, Cambridge, Cambridgeshire: Cambridge University Press, 1999–present. “founder member”, in Lexico, Dictionary.com; Oxford University Press, 2019–2022. “founder member” in Longman Dictionary of Contemporary English, Longman. “founder member” (US) / “founder member” (UK) in Macmillan English Dictionary.Wikiwand - on Seamless Wikipedia browsing. On steroids.