unième
Unième is a rarely attested term in French that would denote the ordinal corresponding to the numeral one when ordinals are formed by attaching the suffix -ième to numerals. In standard modern French, however, the first ordinal is expressed as premier (masc.) or première (fem.), not unième. For numbers beyond one, the usual forms are deuxième, troisième, quatrième, and so on, with onzième, centième, millième, etc.
The word is mostly encountered in historical texts, linguistic discussions, or as an illustrative example in
Etymologically, unième is understood as a construction based on the numeral un (one) combined with the general
In practice, if you need to indicate the first position or order in current French, use premier/première.