IPA: /ˌmɒnəˈmɔːfɛmɪk/
KK: /mɑnəˈmɔrfɛmɪk/
Made up of just one basic unit of meaning, which cannot be broken down into smaller parts.
The word 'cat' is monomorphemic because it cannot be divided into smaller meaningful parts.
Monomorphemic → It is formed from "mono-" (meaning single or one) and "morpheme" (from Greek "morphe", meaning form or shape) and the suffix "-ic" (meaning pertaining to). The word describes a linguistic unit that consists of a single morpheme, indicating it has only one form or shape.
Think of 'mono-' meaning single and 'morpheme' referring to a form — so monomorphemic describes something that has only one form.