The form of the word Elohim, with the ending -im, is plural and masculine, but the construction is usually singular, i.e. it governs a singular verb or adjective when referring to the Hebrew god, but reverts to its normal plural when used of heathen divinities (Psalms 96:5; 97:7). There are many theories as to why the word is plural:
In one view, predominant among anthropomorphic monotheists, the word is plural in order to augment its meaning and form an abstraction meaning "Divine majesty".
Among orthodox Trinitarian Christian writers it is sometimes used as evidence for the doctrine of the Holy Trinity.
In another view that is more common among a range of secular scholars, heterodox Christian and Jewish theologians and polytheists, the word's plurality reflects early Judaic polytheism. They argue it originally meant "the gods", or the "sons of El," the supreme being. They claim the word may have been singularized by later monotheist priests who sought to replace worship of the many gods of the Judean pantheon with their own singular patron god YHWH alone.