Old English bihaldan (West Saxon behealdan) "give regard to, hold in view," also "keep hold of; belong to," from be- + haldan, healdan (see hold (v.)). Related: Beheld; beholding. A common West Germanic compound, compare Old Saxon bihaldan "hold, keep," Old Frisian bihalda "hold, possess, keep, protect, save," Old High German bihaltan, German behalten, but "[t]he application to watching, looking, is confined to English" [OED]. Related: Beholding.
<a href="https://www.etymonline.com/word/beholder">Etymology of beholder by etymonline</a>
Harper, D. (n.d.). Etymology of beholder. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/beholder