Sentence:  Some ſay, compar'd to Bononcini, / That Mynheer Handel's but a Ninny; / Others aver, that he to Handel / Is ſcarcely fit to hold a Candle: / Strange all this Difference ſhould be, / 'Twixt <WSD>Tweedle-dum</WSD> and Tweedle-dee! 
Meaning of the word marked with <WSD> tags:  One of a pair (the other of the pair being "Tweedle-dee") of nominally different (often: but practically identical) things.