The word elohim is a plural word; in Hebrew the plural form of a noun ends in "im" or "ot."
Elohim is the plural form of "eloah."

From Webster's New World Hebrew Dictionary, Macmillan 1992, p65.
Eloah () nm God
Elohim () nm God

It is interesting to note that even though Elohim is plural, the Hebrew dictionary still translates it "God" instead of "Gods."  This is because the Hebrews know that there is only one Yahweh.

So, why did the Hebrews use the word "Elohim" (plural)?
From Unger's Bible Dictionary, Moody Press 1966 Third Edition, p412:

In Canaan there was a tendency to employ the plural forms of deities Ashtoreth (Ashtoroth), Asherah (Asherim), Anath (Anathoth) to summarize all the various manifestations of this deity.  In like fashion the Canaanite plural Elohim ("gods") was adopted by the Hebrews to express all the excellencies and attributes of the one true God.  M. F. U.

Again from Unger's Bible Dictionary:

p311 Elohim (e-lo-him); Heb. plural 'elohim; singular eloah, mighty),...
p293 El (el) ...El is a generic name for God in Northwest Semitic (Hebrew and Ugaritic), and as such it is also employed in the Old Testament for heathen deities...  The original generic term was 'ilum, which dropping the mimation and the nominative case ending "u" became el in Hebrew.  The word is derived from the root "wl, "to be strong, powerful," meaning "the strong one."... El was the head of the Canaanite pantheon.

I do not think that Abraham (Abram), before leaving Ur, ever used the words "El" or "Elohim" in referring, or calling out to, Yahweh; but I can not prove it.  The oldest manuscripts that have been found only go back a few hundred years B.C.E.  The oldest copy of a complete Bible (Leningrad Codex) was found in a geniza in Cairo, Egypt in 1008 C. E.  Much later there were thousands of fragments of older Scriptures found at the same site, but these have been sitting in the Cambridge Museum in England for over 100 years waiting to be restored and translated.  All of the existing Hebrew manuscripts use El or Elohim.

I personally believe that there was originally no generic word for Yahweh, and that the Canaanite exposure caused this concept to be permanently planted into the Hebrew language.

Some people will not use the words "El" and "Elohim" due to the Canaanite origin.  Is it wrong for us to refer to Yahweh with a generic word like "El," "Elohim," or "God?"  "El" and "Elohim" are the Hebrew generic word for a "mighty one;" and "God" is the current English generic word for a "mighty one."  Consider the following:

Eloi (e-lo'i; Aramaic for My God, derived from El).
Mark 15:34 (KJS) And at the ninth hour {Yahshua} cried with a loud voice, saying, Eloi, Eloi, lama sabachthani? which is, being interpreted, My God, my God, why hast thou forsaken me?

Here the Messiah used "El," the generic word for a "mighty one," to refer to his father, Yahweh!