monotreme monotrematous • monotremous · · · Info · Definitions · Synonyms · Characters · · monotreme · · Text Latin · · Script 9 · · Length 3 · · Syllables Definitions · · · (noun) the most primitive mammals comprising the only extant members of the subclass Prototheria. Synonyms: egg-laying mammal. · · Noun Definition 1 Synonyms · · · egg-laying mammal · · Synonym 1 Characters · · e latin small letter e U+0065 m latin small letter m U+006D n latin small letter n U+006E o latin small letter o U+006F r latin small letter r U+0072 t latin small letter t U+0074