From either bitill or bitull + -aðr. <span class="searchmatch">bitlaðr</span> (not comparable) bitted, bridled Zoëga, Geir T. (1910) “<span class="searchmatch">bitlaðr</span>”, in A Concise Dictionary of Old Icelandic...
(“helmed; having a helmet”) Old Norse terms suffixed with -aðr aldraðr <span class="searchmatch">bitlaðr</span> faxaðr fiðraðr fjaðraðr fjǫlhǫfðaðr hjalmaðr jǫklaðr lekaðr nafaðr sakaðr...