Exodus 8:2

ותעל הצפרדע AND THE FROGS (lit. frog) CAME UP — Really there was only one frog, but when they struck at it, it was split into many swarms. This is a Midrashic explanation of the usage of the singular noun here (cf. Sanhedrin 67b; Exodus Rabbah 10:4). But as a literal explanation one must say that the swarm of the frogs is denoted by the singular form. Similar is, (v. 14) “and there was the כנם” — the swarm of insects, in old French pedulier; i. e. a swarm of lice. So, too, here, ותעל הצפרדע means: and there came up a grenouillière (old French) i. e. a swarm of frogs.

וַיֵּ֤ט אַהֲרֹן֙ אֶת־יָד֔וֹ עַ֖ל מֵימֵ֣י מִצְרָ֑יִם וַתַּ֙עַל֙ הַצְּפַרְדֵּ֔עַ וַתְּכַ֖ס אֶת־אֶ֥רֶץ מִצְרָֽיִם׃

And Aharon stretched out his hand over the waters of Miżrayim. And the frogs came up, and covered the land of Miżrayim.