The headword is a preposition (here with nu-movable); see generally LSJ s.v. propa/roiqe. Among other Homeric instances, it is attested at Homer, Iliad 3.22 (web address 1), where Menelaus confronts Paris in front of the assembled throng of Argive warriors. Without nu-movable, it occurs at Homer, Iliad 2.92 (web address 2), with scholion (= D scholia), and many times thereafter; cf. Cunliffe s.v. propa/roiqe(n), p. 345.
[1] The gloss is mainly an adverb, but also functions as a preposition with the same meaning as the headword; see generally LSJ s.v. The lemma is identically glossed by Photius’ Lexicon (pi1280 Theodoridis), the Synagoge, Etymologicum Gudianum 481.46, and Lexica Segueriana 349.30; cf. e.g. ps.-Zonaras 1589.12-14 and Etymologicum Magnum 689.55-690.4 (Kallierges).