This rare nominalized use of the Latin adverb appears in English only from the late sixteenth-century, and is unattested in Continental French or medieval Latin.
s.
1lawpostea, record of trial proceedings and verdict:
(
1310
)
L’atturné: ‘Sire, jeo suy nul bille, qar jeo bailla a mon mestre’ – Hervy: ‘Qei voudriez vous adonqe?’ – L’atturné: ‘Sire, jeo prie un postea’
Ed II iv 195
(
1341
)
Et il continua cele suyte en roulle par posteas
15 Ed III 45