noun

• (figuratively) A clump or portion of something.
  "I found myself truly moved by a stage event for the first time in years. I found myself humming tunes that one might not rightfully call tunes. Days later, I still remember these musical phrasings in little swatches of sound."
• (figuratively) A demonstration, an example, a proof.
  "Pray Sir, pay off the Old Debt, before I truſt you more New. This is a Swatch of Your Faith, and how much You are a Man of Your Word."
• (Northern England, obsolete) A tag or other small object attached to another item as a means of identifying its owner; a tally; specifically the counterfoil of a tally.
  "ITEM that the said Clerkis of the Brevements entre all the Taillis of the Furniunturs in the Jornall Booke in the Countynghous every day furthwith after the Brede be delyveret to the Pantre and then the Stoke [i.e., main part] of the Taill to by delyveret to the Baker and the Swache to the Pantler. … ITEM that the said Clerkis of the Brevements entre all the Taills of the Brasyantors in the Jornall Booke in the Countynghous at every tyme furthwith after the Bere be delyveret into the Buttry and then the Stoke of the Taill to be delyveret to the Brewar and the Swatche to the Butler."

noun

• (UK) A channel or passage of water between sandbanks, or between a sandbank and a seashore.
  "It muſt be obſerved, that the paſſages, called Cockerlees, are no other than ſwatches through the Long-Sand."