Today's OED antedating: "to cover up"

To cover up, to conceal or obscure a blunder or misdeed ("cover," v.1, sec 22 (d), first use cited 1942): Play titled The Front Page, by Ben Hecht and Charles MacArthur, 1928, act I: "MRS. SCHLOSSER. ... You know where he is, you’re just covering up for him."