Lewis & Short

Pĕlŏponnēsus, i, f., = Πελοπόννησος (the island of Pelops), the Peloponnesus, the southern part of Greece, so named from Pelops, who settled there, the modern Morea, Mel. 2, 3, 3; 4; 7; 8; 2, 7, 10; Plin. 4, 4, 5, § 9; Cic. Rep. 2, 4, 8; id. Tusc. 3, 22, 53; id. Fam. 7, 28, 1.
Prov.: nos juveni, ut rogas, suppeditabimus et Peloponnesum ipsam sustinebimus, i. e. will exert ourselves to the utmost, will try to make impossibilities possible (cf. the Greek proverb. Ἀρκαδίαν μ’ αἰτεῖς, μέγα μ’ αἰτεῖς), Cic. Att. 10, 12, 7; cf. id. ib. 10, 5, 2.
Hence,

  1. A. Pĕlŏponnensis, e, adj., Peloponnesian.
    Subst.: Pĕlŏponnensēs, ĭum, m., the Peloponnesians (post-class.), Just. 13, 5, 16 (Jeep. Peloponnensii); Curt. 4, 3, 16; 4, 13, 29.
  2. B. Pĕlŏponnēsĭăcus, a, um, adj., Peloponnesian: litus, Mel. 2, 7, 16: ora, id. 2, 3, 8: gentes, id. 2, 3, 5: bellum, Cic. Rep. 3, 32, 44; id. Off. 1, 24, 84.
    In plur.: Pĕ-lŏponnēsĭăci, ōrum, m., the Peloponnesians, Mel. 2, 3, 9.
  3. C. Pĕlŏponnēsĭus, a, um, adj., Peloponnesian: civitates, Cic. Att. 6, 2, 3: bellum, Nep. Alcib. 3, 1; Thras. 1, 3: circa Peloponnesia tempora, about the time of the Peloponnesian war, Quint. 12, 10, 4.
    Hence, Pĕlŏponnēsii, ōrum, m., the Peloponnesians, Varr. R. R. 2, 6, 2; Vell. 1, 2, 5.