The headword, presumably extracted from the quotation given, is the accusative singular of the noun meri/ths, partaker; see generally LSJ s.v., and cf. mu 632.
[1] The gloss is the same form as the headword, but from the noun summeristh/s, -ou=, o(; see generally LSJ s.v.
[2] Polybius 4.29.6 (web address 1), concerning the attack on the Achaean city of Kynaitha (also Cynaetha; Barrington Atlas map 58 grid C1; cf. delta 833). In the summer of 220 BCE (Walbank, p. 325), the Aetolians and their allies, Illyrian raiders led by the Illyrian prince and privateer Scerdilaidas (later king of Illyria from ca. 211; died ca. 205; OCD(4) s.v.; Wilkes, p. 170; and Edwards, et al., p. 475) overwhelmed and brutally sacked the city. Reneging on a prior agreement with Scerdilaidas, however, the Aetolians retained the impressive booty in its entirety. Chagrined at this betrayal and tempted later that winter by the promise of a twenty-talent yearly stipend (cf. epsilon 3960 (end)), Scerdilaidas turned against the Aetolians and joined forces with Philip V of Macedon (238-179; OCD(4) s.v. Philip(3) and Walbank, p. 477).