The compound adjective 'then-existing' is a modern analytical formation, combining the native English temporal marker 'then' with the participial form of the verb 'exist'. 'Then' originates from a common Germanic demonstrative and temporal adverb, rooted in Proto-Indo-European to- (demonstrative pronoun). 'Exist' entered English from Latin exsistere, meaning "to stand forth, emerge, be", itself from ex- ("out") + sistere ("to cause to stand"). The logical construction is transparent: it literally describes something "that was existing at that then-referenced time", creating a precise phrasal adjective often used in historical, legal, or descriptive contexts to distinguish past conditions from present ones.

Structure: then (time) + existing (state) - then: From Old English þonne, þænne, related to time and sequence. In this compound, it functions as a temporal adverb specifying a past period. - existing: From Latin exsistere ("to step out, appear, exist"), via Old French. The suffix -ing forms the present participle, here used adjectivally to denote a state of being.