JAR, a vessel of simple form, made of earthenware, glass, etc., with a spoutless mouth, and usually without handles. The word came into English through Fr. jane or Span, jarra, from Arab, jarrah, the earthenware vessel of Eastern countries, used to contain water, oil, wine, etc. The simple electrical condenser known as a Leyden Jar (q.v.) was so called because of the early experiments made in the science of electricity at Leiden. In the sense of a harsh vibrating sound, a sudden shock or vibrating movement, hence dissension, quarrel or petty strife, " jar " is onomatopoeic in origin; it is also seen in the name of the bird night- jar (also known as the goat-sucker). In the expression " on the jar " or " ajar," of a door or window partly open, the word is another form of chare or char, meaning turn or turning, which survives in charwoman, one who works at a turn, a job and chore, a job, spell of work.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)