jackanapes.

From Middle English iack napys, iac nape, iac napes (“derogatory nickname of the English military commander and statesman William de la Pole, 1st Duke of Suffolk (1396–1450)”), probably from Jacun or Jakin (“pet forms of the male name Jack”) + ape (“ape, monkey”) + -s (possibly modelled after surnames such as Hobbes and Jakkes), referring to Suffolk’s heraldic badge which was an ape’s chain and clog (“weight such as a block of wood or log attached to an animal to hinder motion”) (see the image, right). It is uncertain whether the word was first coined as a nickname for Suffolk (the earliest known uses), or to refer to an ape or an ape-like person. If the word was originally a nickname, some early uses of etymology 1 sense 2.1 (“person thought to behave like an ape or monkey”) may allude to Suffolk who was widely regarded as an upstart, having risen from the merchant class. In later uses, the middle element of the word was often treated as the indefinite article a or an, that is, as if the word meant “Jack, an ape”.

From jackanape + -s (suffix forming regular plurals of nouns).