\▐ba-fәl\ vt [prob. alter. of ME (Sc) bawchillen to denounce, discredit publicly] (ca. 1590) A plug or other device inserted in a flow channel to restrict the flow or change its direction. A metal piece so placed in a rollercoater pan to direct the stream or flow of paint to the pick-up roller. Also used to direct air currents in an oven. (Perry RH, Green DW (1997) Perry’s chemical engineer’s handbook, 7th edn. McGraw-Hill, New York).