Appallingly

causing dismay or horror:
an appalling accident; an appalling lack of manners.
contemporary examples

when my father approached, he saw that both looked “appallingly young.”
my father, the inglourious basterd kim masters august 8, 2009

his course managed to be both dreadfully dull and appallingly difficult, with few light moments.
stonewall jackson, vmi’s most embattled professor s. c. gwynne november 28, 2014

they are ludicrous insinuations on which the administration and democratic leadership were uniformly and appallingly silent.
‘oops,’ first debate, ‘47 percent’ & more 2012 election turning points mark mckinnon november 5, 2012

rich and poor despise each other, and all justify their meanness in the most appallingly self-serving ways imaginable.
‘the casual vacancy’ review: j.k. rowling cuts loose from harry potter malcolm jones september 26, 2012

however, cases involving violence against women have a traditionally—and appallingly—low rate of conviction in india.
the despicable persistence of the dowry in india nish-ta jha august 3, 2014

historical examples

i admit she is a philistine, appallingly ignorant, and her taste in art is false.
where angels fear to tread e. m. forster

their fitness for purposes of vengeance was appallingly complete.
victory joseph conrad

the deliberations of this ominous court proved to be appallingly short.
astounding stories, march, 1931 various

fortunately milton’s verse is not appallingly great in amount.
the booklover and his books harry lyman koopman

you are the most appallingly irresponsible man whose hands have ever grasped power.
destiny charles neville buck

adjective
causing extreme dismay, horror, or revulsion
very bad
adj.

1620s, present participle adjective from appall. colloquial weakened sense of “distasteful” is attested from 1919.