Lewis & Short

pĕr-angustus, a, um, adj., very narrow (good prose): fretum, Cic. Verr. 2, 5, 66, § 169: aditus, Caes. B. G. 7, 15; Curt. 3, 4, 4: via, Liv. 22, 4: semita, Curt. 7, 11, 1: termini Macedoniae, Just. 7, 1, 2.
Adv.: pĕrangustē, very narrowly, Cic. de Or. 1, 35, 163.