1) Impossible to account for 2) Incomprehensible 3) Inexplicable 4) Unexplainable 5) Unexplained 1) Incomprehensible 2) Inexplicable 3) Irresponsible 4) Strange 5) Unexplainable 
• (a.) Not to be accounted for; inexplicable; not consonant with reason or rule; strange; mysterious. • (a.) Not accountable or responsible; free from control.
[adj] - free from control or responsibility 2. [adj] - not to be accounted for or explained
unaccountable 1. Not answerable or responsible to anyone. 2. Impossible to explain or to give a reason for doing something. 3. Free from accountability; not responsible: 'He was an executive unaccountable to anyone except the president.'
unexplainable adjective not to be accounted for or explained; `perceptible only as unaccountable influences that hinder progress`; `an unexplainable fear`
impossible to account for; unexplained; inexplicable: The boat has an unaccountable tendency to yaw. · exempt from being called to account; not answerable:subordinate, he is unaccountable for errors in policy. As a