Al-ilāhu means deity identified by the identifier Allah, ‘That Which’—The Sublime The Grandiose—is worthy of worship, and the rest i.e. what is not Allah, are worshippers for IT/Him without exception. The plural of Al-ilāhu is Al-Ālihatu meaning idols and such naming is in place due to the people’s belief that worshipping an idol can deify the object into a consequent-god and the naming of the idols are the direct consequence of such worship and not anything of the idol’s essence in and of itself.

لسان العرب

الإلَهُ: الله عز وجل، وكل ما اتخذ من دونه معبوداً إلَهٌ عند متخذه، والجمع آلِهَةٌ. والآلِهَةُ: الأَصنام، سموا بذلك لاعتقادهم أَن العبادة تَحُقُّ لها، وأَسماؤُهم تَتْبَعُ اعتقاداتهم لا ما عليه الشيء في نفسه

The origins of the word Al-ilāhu is from Aliha/Ya’lahu meaning bewilderment when the slave is perplexed by the Divine Attributes and his mental faculties fail him to understand, loathes people’s presence until such limit where he desires nothing and no one within his heart—loves no one but Allah the Singleton deity worthy of love/worship.

وأَصله من أَلِهَ يَأْلَهُ إذا تَحَيَّر، يريد إذا وقع العبد في عظمة الله وجلاله وغير ذلك من صفات الربوبية وصَرَفَ وَهْمَه إليها، أَبْغَضَ الناس حتى لا يميل قلبه إلى أَحد

And this name Allah, within the language of the Arabs, does not allow for derivation of composite forms as does the other Divine Names e.g. Rahman or Rahim.

وليس هو من الأَسماء التي يجوز منها اشْتقاق فِعْلٍ كما يجوز في الرحمن والرحيم

Some others said the origin of the Al-ilāhu is Wilāhin meaning the creation seek IT/Him for all their needs, and they complain to IT/Him for all that hurts them, linguistically as every child goes to the mother for all needs for all complaints.

وأَصل إلَهٍ وِلاهٌ، فقلبت الواو همزة كما قالوا للوِشاح إشاحٌ وللوِجاحِ وهو السِّتْر إِجاحٌ، ومعنى ولاهٍ أَن الخَلْقَ يَوْلَهُون إليه في حوائجهم، ويَضْرَعُون إليه فيما يصيبهم، ويَفْزَعون إليه في كل ما ينوبهم، كم يَوْلَهُ كل طِفْل إلى أُمه

In summary, roots of the word Allah refer to bewilderment for some Divine Being that perplexes all senses and minds, worthy of worship and all else are worshippers. Also the word has the sense of a Beloved, someone the worshippers love passionately and within their hearts there is no other love