Wax lyrical

Origin

“Wax” itself is an ancient word, rooted in the Old English 'weaxan', meaning 'to grow' or 'to become'—think of a 'waxing moon' swelling to fullness. By the 19th century, this old verb was still in active use to denote a transition into a particular state. “Lyrical,” on the other hand, harks back to the lyre, the stringed instrument accompanying ancient Greek lyric poetry, which was intensely personal and emotional. When these two terms converged, "wax lyrical" painted a picture of someone whose speech or writing was growing into a state of poetic, passionate, and often elaborate expression. It captures the essence of words welling up with emotion, expanding like a tide, as the speaker becomes fully immersed in their subject.