Etymology tree
English dull
Middle English -ly
English -ly
English dully
From dull + -ly.
Meanings
In a dull manner; without liveliness; without lustre.
The parson, all unaware, dully pursued his calling, perched above the exquisite derision of their glances. 1930, Norman Lindsay, Redheap, Sydney, N.S.W.: Ure Smith, →OCLC, page 127: