noun

• (ancient history, uncountable) Attachment to, collaboration with, favouring of, or siding with Athens and/or Athenians, especially in the context of the Peloponnesian War (431–404 B.C.E.).
  "The ſame Summer, the Thebans demoliſhed the walles of the Theſpians, laying Atticiſme to their charge."
• (singular only) The prestige dialect of Classical Greek, as spoken and written by the inhabitants of Attica (chiefly Athens) in the fifth and fourth centuries B.C.E.; Attic Greek.
• (singular only) The prestige dialect of Classical Greek, as spoken and written by the inhabitants of Attica (chiefly Athens) in the fifth and fourth centuries B.C.E.; Attic Greek.
• (singular only) The prestige dialect of Classical Greek, as spoken and written by the inhabitants of Attica (chiefly Athens) in the fifth and fourth centuries B.C.E.; Attic Greek.
  "By the Cardinals own confeſsion, this Agapetus liued at Conſtantinople in Iuſtinians time: where it was a great matter for him, no doubt, in ſo long time, to learn to make ſuch a Greek booke as this is; which yet for the ſtile and Atticiſmes, comes a great deale ſhort of Baronius commendation."