From Proto-Indo-European *só (“that”) + -m̥ (compare *sih₂m̥, accusative of *sih₂) + *de ~ *do (demonstrative particle).
*sindos
Irregular | |||
---|---|---|---|
masculine | singular | dual | plural |
nominative | *sindos | *sindou | *sindoi |
vocative | *sinde | *sindou | *sindūs |
accusative | *sindom | *sindou | *sindons |
genitive | *sindī | *sindous | *sindoisom |
dative | *sindūi | *sindobom | *sindobos |
instrumental | *sindū | *sindobim | *sindobis |
feminine | singular | dual | plural |
nominative | *sindā | *sindai | *sindās |
vocative | *sindā | *sindai | *sindās |
accusative | *sindam | *sindai | *sindans |
genitive | *sindās | *sindous | *sindoisom |
dative | *sindai | *sindābom | *sindābos |
instrumental | *? | *sindābim | *sindābis |
neuter | singular | dual | plural |
nominative | *sosim, sinde | *sindou | *sindā |
vocative | *sosim, sinde | *sindou | *sindā |
accusative | *sosim, sinde | *sindou | *sindā |
genitive | *sindī | *sindous | *sindoisom |
dative | *sindūi | *sindobom | *sindobos |
instrumental | *sindū | *sindobim | *sindobis |
While Proto-Celtic did not have articles, reflexes of *sindos came to be used as a definite article (“the”) in descendants, perhaps due to influence from Vulgar Latin (or simply a parallel process as was happening throughout Indo-European). (Can this(+) etymology be sourced?)