In the Arabic language, the proper name of the One Supreme God is Allah. This word usually is taken to mean the One and Only God, but there is a deeper history to this word. It is derived, according to the Arabist Fleisher Franz Delitzsch, from the ancient Arabic root ilah or elah, which means “to be possessed of God.” A derivative from that root term, aliha, means “to be filled with dread” and “anxious to seek refuge,” thus the Qur’an’s call for believers to seek refuge with God from all that they fear. (See 7:200 and 16:98 for example.) The Old Testament Book of Genesis (verses 21:42 & 53) uses the same term where God is called the “fear” or “dread” of Isaac – not in a negative sense, mind you, but in the sense of utter and complete awe. The Hebrew word for God, Eloah (or El), which occurs 3,350 times in the Old Testament, mostly in its plural ‘royal’ form of Elohim, is linguistically related to the Arabic root ilah. Adding the definite article al (the) to ilah makes it al-ilah which is the progenitor of the name Allah, or, The God. If it is remembered that Ishmael, the son of Abraham who dwelled in Arabia, spoke the same ancient tongue as Isaac, whose descendants became the Hebrews, then it is clear why Arabic and Hebrew both have the same linguistic name for God.
Emerick, Yahiya. The Meaning of the Holy Qur’an in Today’s English (p. 827). Unknown. Kindle Edition.