Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
† mĕsŏbrăchys, m., = μεσόβραχυς (sc. pes), a poetical foot of five syllables, of which only the middle one is short (e. g. pulcherrĭmarum; opp. to mesomacros), Diom. p. 479 P.