finial
Any decorative fitting on the corner, end, or top of an object such as a canopy, a fencepost, a flagpole, a curtain rod, or the newel post of a staircase.
The finial is also of timber (probably oak) and is of the rather elaborate type, originally favoured by the London & South Western Railway for its timber masts.
The completion or end of something.
figuratively
But, as the Phœnix on my Front doth gliſter, / Thou ſhalt the Finials of my Frame illuſtre.
Where it comes from
From Late Middle English finial (“(adjective) final; (noun) ornament at the upper extremity of a pinnacle, spire, etc.”) [and other forms], a variant of final (“pertaining to the close or end of something, last, final”), from Old French final (“last, final; definitive”) (modern French final), from Latin fīnālis (“of or pertaining to the end of something, final; of or pertaining to boundaries”), from fīnis (“a border; an end”) (possibly ultimately from Proto-Indo-European *bʰeyd- (“to split”) or *dʰeygʷ- (“to set up; to stick”)) + -ālis (suffix meaning ‘of or pertaining’ to forming adjectives).
Adapted from the Wiktionary entry finial (CC BY-SA 4.0).