The ‘fiver’: Germanic ‘finger’, Balto‐Slavic de‐numeral adjectives in ‐ero‐ and their Indo‐European background

Proto‐Germanic *fingraz ‘finger’ – long connected to PIE *penkʷe ‘5’, but without a convincing derivational scenario – can be interpreted as *pēnkʷ‐ró‐, a genitival R(V̄)‐ó‐ vr̥ddhi derivative to *penkʷerom ‘set of 5’. This latter form is the substantivization of *penkʷero‐ ‘5‐fold, counting 5’ – a form belonging to a series of de‐numeral adjectives which, it is argued, is the single type underlying the Baltic pluralia tantum numerals (Lith. penkerì ‘5.pl.tant’) and the Slavic collectives and distributives (PSl. *pętero ‘group of 5’, *pęterъ ‘5‐fold’). It is further hypothesized that (Post‐)PIE forms like *penkwero‐, *sweḱsero‐, *septm̥mero‐ need not rest upon false segmentation of a thematic derivative of ‘4’ (*kwetwer‐o‐), as is most commonly assumed; rather, they can be explained as simple thematic derivatives of an *‐er locative of the type *penkʷer ‘in/on/at 5’ = ‘in a group of 5’ (a close parallel of this semantic relationship is provided by Lith. arch. trisù ‘3.loc’ = ‘in a group of 3’, or even by French à trois). The posited type *penkʷer also yields a back‐formed substantive *penkʷōr ‘set of 5‐s’, a possible source of the Tocharian B distributive numerals in ‐ār (piśār ‘by 5‐s’