Trip the light fantastic
To dance, especially in an imaginative or ‘fantastic’ manner.
This apparently obscure expression originates from the works of John Milton. In the masque Comus, 1637, he used the lines:
Come, knit hands, and beat the ground,
In a light fantastic round.
By ‘trip’, Milton didn’t mean ‘catch one’s feet and stumble’. The word had long been used to mean ‘dance nimbly’. Chaucer used it that way as early as 1386, in The Miller’s Tale:
In twenty manere koude he trippe and daunce. (In twenty ways could he trip and dance.)
Clearly, Milton was referring to dancing. He must have liked the imagery, as he used it again in the poem L’Allegro, 1645:
Sport that wrinkled Care derives,
And Laughter holding both his sides.
Come, and trip it as you go
On the light fantastic toe.
The ‘light fantastic toe’ was the form that was used when the phrase first circulated, as in this extract from The Times, November 1803:
“A splendid ball was also given; where the CONSUL himself tripped it on the light fantastic toe.”
Source: The Phrase Finder, http://www.phrases.org.uk/meanings/trip-the-light-fantastic.html