Entry 1 sense Webster, 1913 Monocotyledon · Mon·o·cot·y·le·don · IPA /ˌmɒnəˌkɒtɪˈliːdən/ 01 n. A plant with only one cotyledon, or seed lobe; a member of the Monocotyledonae. 1. A plant with only one cotyledon, or seed lobe; a member of the Monocotyledonae.(Bot.)