This important title, often found in connection with name ‘El, is found in several biblical passages in reference to Israel’s God (e.g., Gen.17.1; 28.3; 35.11;49.25; Ex. 6.3; Num. 24.4, 16; Ps. 68.15; Job 8.3,5, etc.).  ‘El-Shaddai is P’s favored title for God before the revelation of the divine name to Moses. But what is its meaning, and what is its historical derivation? Traditionally, following the LXX (i.e., the Septuagint, or ancient Greek translation of the Hebrew Bible), which uses pantokrator, and the Vulgate (a Latin translation of the Bible by St. Jerome), which uses omnipotens, the term has often been rendered in English translation as “Almighty,” but it is now generally considered that this interpretation is fallacious, and possibly stems from a similar sounding Hebrew root $-d-d, meaning “to destroy.” Some modern scholars have suggested several other possibilities, such as connecting it with the Hebrew word $ad, meaning breast. However, since ‘El-Shaddai was a male diety, this seems somewhat unlikely. Another suggestion is that it is related to the Hebrew word sadeh, meaning “field.” However, this root uses a different sibilant (sin) in its root than does Shaddai (shin).
The most widely accepted scholarly view is that ‘El-Shaddai means “El, the mountain one,” relating shaddai to an Akkadian word $adum, “mountain.” Besides being a strong cognate, there are also several other historical factors that seem to lead to this conclusion. For instance, F.M. Cross has noted a Hurrian hymn which specifically describes El as “the one of the mountain.” The word is also used to describe the Amorite deity (Ilu-)Amurru, whose consort is A$ratum, the counterpart of the Canaanite high god ‘El’s consort Athirat (Asherah). Moreover, the Deir ‘Alla instription uses $dyn in parallel with ‘ihn, in reference to the gods of the assembly. Finally, ‘El and his divine assembly met on a mountain.
Given all of these factors then, ‘El-Shaddai very plausibly means “El, the mountain one,” and is most probably originally a divine title or epithet derived from the Canaanite high god ‘El.
 I have relied primarily on John Day’s discussion of this epithet in his section “El-Shaddai” in Yahweh and the Gods and Goddesses of Canaan. Journal for the study of the Old Testament, 265. (Sheffield: Sheffield Academic Press, 2000), 32-34.