"the atmosphere of negative theology, so respectful of the mystery [(l'ambiance mystérique de la théologie négative)], . . . is, as it were, condensed and concentrated in the constant moment, in the incorruptible moment of the theology of eminence, Verbum abbreviatum. This procedure does not render pointless the old debate over the apophaticism of Saint Thomas. . . . But in the end the Word is given, and one touches it with one's hand."
Philippe Vallin, "Henri de Lubac et Saint Thomas d'Aquin: ouverture et structure en théologie," Revue des sciences religieuses 77, no. 2 (2003): 248.
Verbum abbreviatum ("the Man-God, Verbum abbreviatum" (248)) was, apparently, a medieval expression dear to de Lubac (248n96, which cites Histoire et esprit, pp. 345-346). Cf. the verbum [ab]breviatum of Is 10:22-23 and Rom 9:28, as quoted by, for example, Aquinas (Index Thomisticus, Corpus Thomisticum).
Abbreviatum derives from ML se abbreviare, to abase or humble or lower oneself, to stoop down, to condescend, and was used in the context of the theology of the Incarnation (Blaise, Lexicon Latinitatis Medii Aevi (Brepols, 1975), 2). So Verbum abbreviatum would be something like "the Word self-abased", "the Word [who] humbled himself", etc. I'm working not from the texts directly but from Blaise, but Niermeyer gives other senses, too, ones that we today would associate with a term like abbreviare: to summarize, write with abbreviations, shorten, or contract (Niermeyer & Kieft, Mediae Latinitatis lexicon minus, 2nd ed., ed. Burgers (Brill, 2002), 4-5). So the Verbum abbreviatum was probably also "the Word contracted", "the Word sized down", "the Word contained" by the womb of Mary, the crib, etc. (Or so I'm just guessing.)