pinnacle (n.)

c. 1300, "mountain top, sharp peak, promontory," from Old French pinacle "top, gable" (13c.) and directly from Late Latin pinnaculum "peak, pinnacle, gable," extended form (via diminutive suffix, but not necessarily implying smallness) of Latin pinna "peak, point," (see pin (n.)). Figurative use is attested from c. 1400. The meaning "pointed turret on the buttress or roof of a building" is from late 14c.

Its constructive object is to give greater weight to the member which it crowns, in order that this may better resist some lateral pressure. The application of the term is generally limited to an ornamental spire-shaped structure, standing on parapets, angles, and buttresses, and often adorned with rich and varied devices. [Century Dictionary]