Noun. An ornamental projection, characteristic of Gothic architecture, seen at regular intervals on canopies, windows, gables, etc.. The ornament typically consists of the form of a leaf that curves up and away from the supporting surface and returns partially upon itself, generally a winding stem like a creeping plant, with flowers or leaves projecting at intervals, and terminating in a finial:
The above image is from Wikipedia. Crockets were often placed "in suits" and spaced an equal distance apart.
They are also used to decorate the capitals of columns, where they are termed 'crocket capitals':
(the above image is from http://www.pitt.edu/~medart/menuglossary/crocket.htm)
A set of crockets, here on Memorial Tower at the University of Missouri:
Another showing crockets along a capital:
Adjective. 'crocketed' - (of a gable or spire) furnished with a crocket; "a crocketed spire". Here's an example from the spire of Saint Peters, in Preston England:
(image from Made in Preston's photostream)
As you can see, on the exterior of the building, crockets are generally carved in stone, however they also appear on interior carved woodwork, particularly in chapels and cathedrals.
Derivation: Two related explanations:
1. According to the Online Etymological Dictionary, the word comes frrom Middle English croket, ornamental curl of hair, hook, from Old North French croquet, shepherd's crook, diminutive of croque, variant of Old French croche. The word 'crochet' (the knitting art) derives from the same root. The Old French croquet also relates to the word croc, akin to Old Norse krōkr "hook" - the root of another wood-related term crook (of a tree).
2. According to Wikipedia, the name also connects to the diminutive of the French croc, meaning "hook", due to the resemblance of crockets to a bishop's crosier, a stylized staff of office:
The connection between bishops and shepherds being an old one in Christian iconography.