וימש חשך. וְיַחֲשִׁיךְ עֲלֵיהֶם חֹשֶׁךְ יוֹתֵר מֵחֶשְׁכּוֹ שֶׁל לַיְלָה, חֹשֶׁךְ שֶׁל לַיְלָה יַאֲמִישׁ וְיַחֲשִׁיךְ עוֹד: וימש חשך signifies and it (the darkness mentioned in the preceding phrase, ויהי חשך) shall darken for them the natural darkness to a higher degree than the darkness of night: i. e. the darkness of night shall become even more black and dark.
וימש. כְּמוֹ וְיַאֲמֵשׁ; יֵשׁ לָנוּ תֵבוֹת הַרְבֵּה חֲסֵרוֹת אָלֶ"ף, לְפִי שֶׁאֵין הֲבָרַת הָאָלֶ"ף נִכֶּרֶת כָּל כָּךְ, אֵין הַכָּתוּב מַקְפִּיד עַל חֶסְרוֹנָהּ, כְּגוֹן "וְלֹא יַהֵל שָׁם עֲרָבִי" (ישעיהו י"ג), כְּמוֹ לֹא יַאֲהֵל – לֹא יַטֶּה אָהֳלוֹ, וְכֵן "וַתַּזְרֵנִי חַיִל" (שמואל ב' כ"ב), כְּמוֹ וַתְּאַזְּרֵנִי; וְאֻנְקְלוֹס תִּרְגֵּם לְשׁוֹן הֲסָרָה, כְּמוֹ לֹא יָמוּשׁ; "בָּתַר דְּיֶעְדֵּי קְבַל לֵילְיָא" – כְּשֶׁיַּגִּיעַ סָמוּךְ לְאוֹר הַיּוֹם; אֲבָל אֵין הַדִּבּוּר מְיֻשָּׁב עַל הַוָּי"ו שֶׁל וְיָמֵשׁ, לְפִי שֶׁהוּא כָתוּב אַחַר וִיהִי חֹשֶׁךְ. וּמִ"אַ פּוֹתְרוֹ לְשׁוֹן "מְמַשֵּׁשׁ בַּצָּהֳרַיִם" (דברים כ"ח), שֶׁהָיָה כָפוּל וּמְכֻפָּל וְעָב עַד שֶׁהָיָה בוֹ מַמָּשׁ: וימש means as much as (is a contraction of) ויאמש (a Hiphil form of אמש, evening darkness). We have many words in which an א is omitted; since the sound of the א is not very marked, Scripture is not particular about omitting it. An example is: (Isaiah 13:20) “the Arabian לֹא יַהֵל there”, which is the same as לא יַאֲהֵל, shall not pitch his tent. Similar is, (II Samuel 22:40) “וַתַּזְרֵנִי with strength”, which is the same as וַתְּאַזְרֵנִי “And thou hast girded me” (cf. Psalms 30:12). Onkelos translated it in the sense of removing, from the same root as, (Joshua 1:8) “it shall not depart (ימוש)”, his rendering being, “[and there shall be darkness..] after the darkness of night has departed”, i. e. when the time approaches near to the light of day. But the statement does not then fit with the ו of וימש, because this word is written after ויהי חשך. A Midrashic statement explains it in the sense of (Deuteronomy 28:29) “groping (ממשש feeling) at noon-day”, so that the meaning would be that it was of such a double character and so thick that there was something tangible in it (Exodus Rabbah 14:1-3).