Wax lyrical

Meaning: Speak enthusiastically and poetically about something

Explanation: This expression derives from the verb ‘to wax’, meaning ‘to grow’. In modern English, it is only used to describe the increase of the moon’s size in the night sky, but in days gone by it commonly referred to growth. The phrase itself first appeared as ‘wax eloquent’ in an 1824 text, and subsequently took its contemporary form, ‘wax lyrical’, in the 20th century.

Example:Sarah recently came back from Venice and has been waxing lyrical about it all afternoon.