'apostolicalness' originates from Late Latin, specifically the word 'apostolicus', where the Greek root 'apostolos' meant 'one sent out' (a messenger or envoy).

'apostolicalness' evolved from Middle English 'apostolical' (an adjectival form), which in turn derived from Late Latin 'apostolicus' (from Greek 'apostolos'); the noun-forming suffix '-ness' was later added in English to create 'apostolicalness'.

Initially, related words meant 'pertaining to an apostle or the apostles' (i.e., 'relating to one sent out'), but over time the form 'apostolicalness' came to denote specifically the abstract quality or state of being apostolical.