An Etymological Dictionary of Astronomy and Astrophysics

1. A small piece of material used to mend a tear or break, to cover a hole, or to strengthen a weak place.
   

   2. A piece of material used to cover or protect a wound, an injured part, etc.
      

   3. A small piece, scrap, or area of anything (Dictionary.com). → bald patch; → patchy turbulence.

Etymology (EN): M.E. pacche; of uncertain origin.

Etymology (PE): Pac, from Bašgaridi (Giroft) pac “patch; fragment,” probably from *parka-, from *par- “piece” + diminutive/relation suffix -ka; cf. pâré “piece, part, portion;” parré “portion, segment (of an orange);” pargâlé “piece, portion; patch;” Kermâni pariké “portion, half;” Tabari perik “minute quantity, particle;” Lârestâni pakva “patch;” Borujerdi parru “patch;” (Fin Bandar Abbâs) park “patch;” (Tâti) pajina “patch, darn;” → part.