"persecuting giant" in the Holy Saturday canon?

The irmos of the first ode in the canon that was read for both Holy Saturday matins and the midnight office before Paschal matins:

The One, who of old hid the pursuing tyrant in the waves of the sea, the children of those he saved have hidden beneath the earth; but let us, like the young maidens, sing to the Lord; for he has been greatly glorified.

At least, that seems to be the kind of translation I've seen in print and online. But as we sang it in church, I believe "pursuing tyrant" was replaced with "persecuting giant." Now, "pursuing tyrant" makes me think of Pharaoh at the Red Sea crossing. But when I heard it in church, I couldn't begin to think who this "persecuting giant" was. The usual translation looks more faithful to the Greek edition that I found online, but I don't read Slavonic. Anyone know where the "persecuting giant" comes from?