Extended Strong's Greek Lexicon (Abbott-Smith based)
something to grasp
Usage: ἁρπαγμός, οῦ, ὁ (ἁρπάζω); __1. prop., accusative, to the rule of its formation (Bl., § 27, 2), actively, the act of seizing, robbery (Plut., Deu Puer. Educ., p. 12A), Php.2:6, AV (Waterland, Works, II, 108; Cremer, 649 f.; Meyer, in l; cf. also JThS, July, 1909, April, 1911; MM, see word). __2. Passively = ἅρπαγμα (Eze.22:25, of a lion's prey, ), a thing seized, hence, a prize: Phi, l.with, RV (Lft., Ellic., ICC, in l; Donaldson, NCrat., 450 ff.; and esp. Gifford, The Incarnation, 59-71, and reff.
in DB, ii, 835 B). The lexical data favour the active meaning, but as they also admit the possibility of the alternative, most modern expositors have accepted the latter as seeming to suit the logic of the passage better. The lexical difficulty, however, remains (MM, see word, esp. the last ref.). As to the usage of St. Paul, he seems inclined to adopt the -μα form where it is appropriate (e.g. Rom.11:9, where cf. LXX;
1Co.13:9, 2 Co 19), and there is certainly a presumption in favour of the active meaning here from the fact that he does not use the LXX ἅρπαγμα. Suggestions looking to a fresh exegesis are given in JThS, ll with† (AS)