mesencephalon mesencephalic • mesenchyma · · · Info · Definitions · Synonyms · Characters · · mesencephalon · · Text Latin · · Script 13 · · Length Definitions · · · (noun) the middle portion of the brain. Synonyms: midbrain. · · Noun Definition 1 Synonyms · · · midbrain · · Synonym 1 Characters · · a latin small letter a U+0061 c latin small letter c U+0063 e latin small letter e U+0065 h latin small letter h U+0068 l latin small letter l U+006C m latin small letter m U+006D n latin small letter n U+006E o latin small letter o U+006F p latin small letter p U+0070 s latin small letter s U+0073