ARGILLACEOUS Meaning of ARGILLACEOUS in English [ ˌα:dʒɪ'leɪʃəs ]■ adjective Geology (of rocks or sediment) consisting of or containing clay.OriginC17: from L. argillaceus (from argilla 'clay') + -ous . Concise Oxford English vocab. Сжатый оксфордский словарь английского языка. 2004