Source : Webster's Revised Unabridged Dictionary (1913)

Insignificantly \In`sig*nif"i*cant*ly\, adv.
   without significance, importance, or effect; to no purpose.
   ``Anger insignificantly fierce.'' --Cowper.

Source : WordNet®

insignificantly
     adv 1: in an insignificant manner; "some people living
            insignificantly among us"
     2: not to a significant degree or amount; "Our budget will only
        be insignificantly affected by these new cuts" [ant: {significantly}]