finial

Especially in Gothic architecture: an ornament, often in the form of a bunch or knot of foliage, on the peak of the gable of a roof, a pediment, a pinnacle, etc.

• His [Butades'] invention it vvas to ſet up Gargils or Antiques at the top of a Gavill end, as a finiall to the creſt tiles, vvhich in the beginning he called Protypa.
• From this fair Palace then he takes his Front, / From that his Finials; […] / And ſo, ſelecting euery vvhere the beſt, / Doth thirty Models in one Houſe digeſt.

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.broadly

• 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.
• It was a narrow, gravelled island we had to lie on, guarded by glazed brick chimneys and, running along the sides, a prickly little gothic fence of iron finials and terracotta quatrefoils.

The completion or end of something.alsoattributivefiguratively

• But, as the Phœnix on my Front doth gliſter, / Thou ſhalt the Finials of my Frame illuſtre.
• [T]hey have invented idols, a manifest advance toward that polytheism and pantheism which lead through a triad and duad of deities to monotheism, the finial of the spiritual edifice.