Another interpretation: Hiroth means nothing other than the place of their freedom (heruth). The place of Atlas, the place of their house of idolatry. Formerly it was called Pithom, as it is said, "and he built store-cities" (Exodus 1:11). Then it changed for them and was called Pi-hahiroth, for it ensnares (or holds back) those who worship it.
Pi-hahiroth the Place of Freedom That Was Once Pithom
Yalkut Shimoni on Torah 230:4
דָּבָר אַחֵר, אֵין חִירֹת אֶלָּא מְקוֹם חֵרוּתָן, מְקוֹם אַטְלָס, מְקוֹם בֵּית עֲבוֹדָה זָרָה שֶׁלָּהֶן לְשֶׁעָבַר הָיָה נִקְרָא פִּיתוֹם, שֶׁנֶּאֱמַר "וַיִּבֶן עָרֵי מִסְכְּנוֹת" וְגוֹ' חָזְרוּ לָהֶן וְנִקְרָא פִּי הַחִירֹת, שֶׁהִיא מְאֲחֶרֶת עוֹבְדֶיהָ.