lusimus: of lyric, especially amatory, verse composition; cf. Catul. 61.232; Catul. 68.17 Hor. Carm. 1.32.1 “si quid vacui sub umbra lusimus tecum, barbite” ; Verg. Ecl. 1.10 “ludere quae vellem calamo agresti” ; Aus. Epist. 7.1 “ut rescriberes ad ea quae ioculariter luseram.”
 convenerat: we had agreed.
 illinc: perhaps meaning only ‘from the contest,’ though more likely indicating that the banquet was not at the house of Catullus.
 postquam: found only here in Catullus with the imperfect, though he uses it with the perfect six times, and with the pluperfect subjunctive in indirect discourse once (Catul. 84.11). In the comedians it occurs only once with the imperfect (Pl. Most. 640), but this use becomes more frequent with Cicero, Sallust, and Livy.
 cavĕ: cf. the same quantity in v. 19 and Catul. 61.152, and frequently in the comedians and later. The verb occurs in Catullus but four times, and yet with three different constructions dependent upon it; the simple subjunctive in this and the following verses, the present infinitive in v. 21, and the subjunctive with ne in Catul. 61.152.
 preces: as expressed in v. 13.
 vehemens: severe, inexorable; cf. Cic. Catil. 4.6.12 “si vehementissimi fuerimus, misericordes habebimur” . The adjective is dissyllabic here, and apparently elsewhere, except in a verse of M. Aurelius to Fronto.