adj

• (often derogatory)
  "a petty fault    petty squabbles"
• (often derogatory)
  "Such literature may well be anathema to those who are too docile and petty for their own good."
• (often derogatory)
  "My cousin is so petty—I forgot his birthday and he's been making snarky comments all week."
• (historical) Of or relating to the lowest grade or level of school; junior, primary.
  "Friends are separated for long portions of time even while they live; at last they take their leave for ever: although, I remember, when you left me in the petty form at Westminster, I soon afterwards found you in a higher remove: and this world is only the petty form of the universe; so I not only expect to pass a social hour with you here, but am in hopes of a merry meeting in a better place; […]"

noun

• (dialectal, euphemistic, informal) An outbuilding used as a lavatory; an outhouse, a privy.
  "If these houses had been built by his Lordship every one would have had his petty, at all events dividing the odour & also having a chance that some of the occupiers would clean out—but a common occupation is nobody's business, unless the owner of all the buildings takes it in hand."
• (historical) A class or school for young schoolboys.
  "[…] I took my seat in what was denominated, "The Idle Class", that is, at the very bottom of the school, where all those who have not received some previous instruction in Latin are placed. I however soon got out of that disgraceful and ignorant form, passed with rapidity and eclat the under and upper petty, and entered into the upper first, […]"
• (obsolete, chiefly in the plural, also figuratively) A little schoolboy, either in grade or size.
  "[S]ome of them, which were the Petties and Punies of that ſchoole, whereof old Martin [Marprelate] was the maſter; though then he was but as ſome blinde and obſcure pariſh Clarke that taught in the Belfrie, not preſuming, as hee doth nowe, to preſſe into the Church, (that place in reſpect of the appurtenances being fitter for him) began but rawly with their little a, b, c."