Adam Clarke on Exodus 1:13

To serve with rigour - בפרך bepharech, with cruelty, great oppression; being ferocious with them. The word fierce is supposed by some to be derived from the Hebrew, as well as the Latin ferox, from which we more immediately bring our English term. This kind of cruelty to slaves, and ferociousness, unfeelingness, and hard-heartedness, were particularly forbidden to the children of Israel. See Lev 25:43, Lev 25:46, where the same word is used: Thou shalt not rule over him with Rigor, but shalt fear thy God.