The headword -- aorist passive participle, masculine nominative singular, of mesolabe/w -- is presumably extracted from the quotation.
[1] Polybius fr. 184 Büttner-Wobst (individuals unidentifiable). For the idiom "cut short/interrupted by fate" see also Diodorus Siculus 1.3.3, 11.26.7, 16.1.5. For (this word for) fate, see pi 1022. Büttner-Wobst notes (538) that Hemsterhusius (Tiberius Hemsterhuys (1685-1766)) -- believing that it should be understood as referring to Philip V of Macedon (238–179 BCE; cf. OCD(4) s.v., p. 1129) and his son Perseus (ca. 212-166) -- attributed this fragment to Polybius (ibid.). Although accepting the fragment himself, Büttner-Wobst concedes (ibid.) that Hultsch thought its wording was in fact characteristic of Diodorus Siculus. Walbank agrees that the fragment apparently pertains to Philip and Perseus, but cautions that it is not clearly Polybian (754).