Sentence:  Zygonic relationships, or <WSD>"zygons</WSD>", are depicted using the letter Z. 
Meaning of the word marked with <WSD> tags:  An affinity or connection in a piece of music between tones, chords, or phrases, such that one part appears to repeat, to imitate, or to derive from the other, especially when perceived as an organising principle in the music; a zygonic relationship.