The primary headword is either masculine accusative singular or, more probably, neuter nominative/accusative plural of the adjective a(paca/pas. If the latter, perhaps extracted from the first quotation given; in any event, quoted from somewhere.
[1] This striking gloss invokes a phrase common in the Septuagint and elsewhere; it is often, but not invariably, appended to a word like 'all'.
[2] Procopius, History of the Wars of Justinian 1.25.3 (web address 1), on John the Cappadocian; cf. Kaldellis (68); again at iota 469 (end). See also alpha 2407.
[3] Menander Protector fr. 18.6 Blockley. See already alpha 2330, and again sigma 10; both have "all together", evidently correctly, in the accusative.
[4] Likewise in Photius and other lexica.
[5] A common expression is a(pacaplw=s ei)pei=n "to speak generally." Perhaps the infinitive should have appeared with the adverb here.