noun

• (archaic) An additional adverse event that occurs unexpectedly after an earlier one was thought to be over and done with.
  "[…] immediatly after the Vniuersall deluge, Nimrod […] perswaded the people to secure themselues from the like after-claps, by building some stupendious Edifice, which might resist the fury of a second deluge."
• (archaic) An unfavourable turn of events following a favourable situation; an eventuality for which one ought to be prepared.
  "[…] as cookes among all their sawces doo mind nothing lesse than sobernesse: so these in the abundance of their ioies, thought nothing of afterclaps […]"
• (uncountable, medicine, obsolete) Urethral discharge as a symptom of gonorrhea.
  "[…] I have known instances where the gonorrhœa has ceased without leaving any after-clap, or gleet,"
• (obsolete) A change or attempted change to an agreement after it has been entered into; an additional charge (especially one over and above the previously agreed-upon price).
  "[…] he produced my Accompt in his Book, and very generously crossed it out, but I desired a Receipt to prevent any After-claps, which he readily granted, and then I very lovingly took my Leave of him."

noun

• (South Africa, historical) A canvas curtain or tailboard at the rear of a covered wagon.
  "And now the “after-clap” of the wagon was hurriedly drawn aside, and three young faces were seen peeping forth."