Exodus 2:3

ולא יכלה עוד הצפינו AND SHE COULD NO LONGER CONCEAL HIM, because the Egyptians calculated the period from when he (Amram) took her back. She, however, bore him after a term of six months and one day — for a woman who gives birth to a child in the seventh month may do so in incomplete months (i. e. the seventh month of pregnancy may not be completed) (Niddah 38b) — and they (the Egyptians) made enquiry regarding her at the end of nine months (the normal term of pregnancy, but in this case three months after the child’s birth; therefore “she could no longer conceal him”). גמא PAPER-REED — In the language of the Mishna it is called גמי (Shabbat 78a), and in old French junc. It is a flexible substance that offers resistance to the pressure of both soft and hard things (Sotah 12a). בחמר ובזפת — with pitch (זפת) outside, but with slime (חמר) inside, in order that that righteous child might not smell the disagreeable odour of the pitch (Sotah 12a). ותשם בסוף AND SHE PUT IT IN THE FLAGS — It (סוף) has the same meaning as אגם. old French rosel. Another example of the word is (Isaiah 19:6) “And reeds and flags (סוף) shall wither”.

וְלֹא־יָכְלָ֣ה עוֹד֮ הַצְּפִינוֹ֒ וַתִּֽקַּֽח־לוֹ֙ תֵּ֣בַת גֹּ֔מֶא וַתַּחְמְרָ֥הֿ בַחֵמָ֖ר וּבַזָּ֑פֶת וַתָּ֤שֶׂם בָּהּ֙ אֶת־הַיֶּ֔לֶד וַתָּ֥שֶׂם בַּסּ֖וּף עַל־שְׂפַ֥ת הַיְאֹֽר׃

And when she could not longer hide him, she took for him a box made of papyrus, and daubed it with slime and with pitch, and put the child in it; and she laid it in the rushes by the River’s brink.