denominator

Understanding Bob Dylanを読んでいます。
Among the most common images in Dylan's songs are the door, the window, the gate and the hallway. Like the lines and the tracks, they are usually barriers or boundaries that separate the singer from others, or that prevent his moving on, or creating. So common is their use - and perhaps now their overuse - that they are another common poetic denominator of Dylan's songs. It would be odd to hear a Dylan song which didn't have a highway, door or a window in it.
上の引用箇所に出てきた "denominator" ですが、数学用語の意味しか頭に浮かびません。　辞書を見ます。
・Merriam-Webster's Online Dictionary:
a) a shared trait: a common denominator
b) the average level (as of taste or opinion)
次の辞書に詳しい説明がありました。
・V2 Vocabulary Building Dictionary: a common characteristic or shared quality: It seems like movies today are developed for the lowest common denominator. (common trait, divisor)
Tips: In math, a denominator is the number that appears at the bottom of a fraction. The number 4 is the denominator in the following fractions: 1/4, 2/4, 3/4. When you hear the term "common denominator," it refers to that which several different people or things have in common. For example, in the fractions previously listed, the common denominator is the number 4. This is where the idea comes from. You may have heard the phrase "lowest common denominator." This often refers to the large number of people who will accept bad quality products.
なるほど、"common denominator" のフレーズも一緒に覚えると良さそうですね。
・Wiktionary: (by extension, figuratively) A trait or attribute that is shared by all members of some category.
Understanding Bob Dylanでもこの後に "common denominator" が次の形で出てきました。
We have attempted to understand the power of Dylan's lyrics through the ways in which he has used common poetic denominators that have been central to modern western literature.