Ibn Ezra

For the leader (el ha-nechilot): [Regarding the preposition] el (אֶל): It is like al (עַל - upon/concerning) in meaning here. Similar [is the usage in (I Samuel 1:10)]: "And she prayed unto/concerning (al) Ad-nai." [And compare (I Samuel 1:27)]: "Concerning (el) this child [I prayed]." [This is] the opposite [of their usual distinction: el normally means 'to/towards' while al means 'upon/about']. And the [letter] Alef (א) does not interchange with the [letter] Ayin (ע), but rather the letters Alef, Heh, Vav, Yod (אהו"י - the weak letters) are the ones that interchange, and [also] Shin (ש) with Samekh (ס), because they are close in their place of articulation. And ha-nechilot (הַנְּחִילוֹת): [This is likely] the beginning [words or tune name] of a liturgical poem/song (piyyut). Perhaps it is derived from the root [N-Ch-L, נ-ח-ל, meaning 'to inherit'], as in [a phrase like (Numbers 34:17)] "they shall divide the inheritance (yinchalu) for you." [The noun formation Nechilot is formed] in the manner of [a segolate noun like (I Kings 19:8)] "ha-achilah ha-hi" (האכילה ההיא - that eating).