The headword adjective is presumably extracted from the quotation given. (For it in another context see under tau 33.)
[1] This quotation comes from no extant source (though Adler's marginal 'E' indicates her belief that it comes from the Excerpta Constantini Porphyrogeniti, claimed by C. de Boor as the source of all the Suda's historical extracts which do not originate from identifiable lexica or scholia).
Two-talent stones were unusually large ones: see generally Eric Marsden, Greek and Roman Artillery: historical development (Oxford 1969) 89-91 (one-talent and thirty-mina sizes the norm). Tracey Rihll, The Catapult: a history (Yardley PA, 2007) registers 'shot-weights' between 4 drachmas and 3 talents.