The dominant theory pertains to the French personal names Huard and Houard adapted after the Norman Conquest of 1066.
It is from a Germanic source similar to Old High German *Hugihard "heart-brave," or *Hoh-ward, literally "high defender; chief guardian."
Also probably in some cases a confusion with cognate Anglo-Scandinavian personal name Haward from Hávarðr, which means ha(r) "high" (or hǫð "battle") and element varðr, meaning "guardian", and sometimes also with unrelated Hayward.
In some rare cases from Old English eowu hierde "ewe herd.
"[2][3][4] In Anglo-Norman the French digramm -ou- was often rendered as -ow- such as couard → coward, tour → tower, flour (western variant form of fleur) → flower, etc (two last examples with svarabakhti, typical of the Anglo-Norman language).