Jamieson, Fausset and Brown on Leviticus 21:4

4. But he shall not defile himself--"for any other," as the sense may be fully expressed. "The priest, in discharging his sacred functions, might well be regarded as a chief man among his people, and by these defilements might be said to profane himself" [Bishop Patrick]. The word rendered "chief man" signifies also "a husband"; and the sense according to others is, "But he being a husband, shall not defile himself by the obsequies of a wife" (Eze 44:25).