inexplicably
Concise Oxford English Dictionary © 2008 Oxford University Press:
inexplicable /ˌɪnɪkˈsplɪkəb(ə)l, ˌɪnɛk-, ɪnˈɛksplɪ-/
▶adjective unable to be explained or accounted for.
– derivatives
inexplicability noun,
inexplicably adverb.
inexplicability noun,
inexplicably adverb.
'inexplicably' also found in these Oxford entries:

