doesn't come from the word shad
- it comes from Shadad
which means "to deal violently with, despoil, devastate, ruin, destroy, spoil" - Shadad
being the primitive root word.
And technically, El-Shaddai is "God Almighty," not just "The Almighty"
El = God (Singular)
Shaddai = Almighty, most powerful
, whilst meaning breast or bosom, comes from the word Shuwd
(pronounced "shood") which means "to ruin, destroy, spoil, devastate".
Maybe because breasts are temptations and therefore can "ruin" a man?
Or perhaps more to the "spoil" variety