The unglossed headword (evidently quoted from somewhere) is aorist indicative passive, third-person plural, of the verb πλινθεύω (on which see pi 1772, pi 1773). This form is unattested outside of lexicography, and no other form of the verb is attested with the connotation ascribed to it here. But a similar gloss of the same form at Lexica Segueriana 253.8-12 (Glossae rhetoricae; cf. Lex.Seg., Δικῶν ὀνόματα 187.27, Etymologicum Magnum 367.43) suggests that the original context was in the corpus of one of the classical Athenian orators.
Note LSJ s.v. πλινθεύω , III: 'Pass. is variously expld. by Gramm. as to be changed into bricks, built up with bricks, tortured or enslaved, EM367.43 etc.; to be duped, Hsch., Suid.'.
[1] In place of the (at best) awkward phrase περὶ οἰκοδόμημα μόνον (translated here as "alone in the confines of a structure") Bekker suggests substituting the participle περιῳκοδομημένον , which would make the Greek a bit more clear and alter the translation as follows: "being shut up by having a structure built around one..." This emendation receives some support from the parallel entry in the Glossae rhetoricae (see note above), where a different form of this verb is employed (περιοικοδομηθέντες ).