Sentence:  ... ill things are like guid—they baith come bit by bit, a <WSD>pickle</WSD> at a time ... 
Meaning of the word marked with <WSD> tags:  A small or indefinite quantity or amount (of something); a little, a bit, a few. Usually in partitive construction, frequently without "of"; a single grain or kernel of wheat, barley, oats, sand or dust.