the word 'thirtieth' is a modern english ordinal number formed by combining the cardinal number 'thirty' with the ordinal suffix '-eth'. 'thirty' itself originates from old english 'þrītiġ', a compound of 'þrīe' (three) and '-tiġ' (a group of ten), reflecting the germanic decimal counting system. the suffix '-eth' descends from the old english ordinal suffix '-oþa', used to denote position in a sequence. this construction follows the standard pattern for forming ordinal numbers from the tens (twentieth, thirtieth, etc.), where the final '-y' of the cardinal number changes to '-ie' before the suffix.

Structure: thirty (cardinal number) + eth (ordinal suffix) - thirty: from old english 'þrītiġ' (three tens), of germanic origin; functional role: cardinal number base. - eth: from old english '-oþa', '-aþa', ordinal suffix; functional role: forms ordinal numbers.