duple vs twain

duple

adj

  • Double. 

  • Having two beats in each foot. 

  • Having two beats, or a multiple of two beats, in each measure. 

twain

adj

  • twofold 

noun

  • pair, couple 

verb

  • To part in twain; divide; sunder. 

How often have the words duple and twain occurred in a corpus of books? (source: Google Ngram Viewer )