Charles Ellicott Commentary Genesis 42:18

"And Joseph said unto them the third day, This do, and live: for I fear God:" — Genesis 42:18 (ASV)

I fear God (Elohim). —By using the name Elohim, they would understand that he worshipped the same God as they did. For though he may himself have used the Egyptian word for the supreme Deity, yet doubtless he would take care that the interpreter used the word Elohim.