unaccountable

adj 1 that cannot be explained or accounted for 无法解释的; 难以说明的: an unaccountable increase in cot deaths, ie of babies 难以解释的婴儿猝死数量上升的现象 * For some unaccountable reason, the letter never arrived. 不知何故, 那封信始终未收到. 2 ~ (to sb/sth) (fml 文) not answerable for one's actions, etc; not accountable （对自己的行为等）不必负责任的, 无责任的.

umbilical cord, umbilicus, umbra, umbrage, umbrella, umlaut, umpire, umpteen, umpteenth, un, un-, un-American, unabashed, unabated, unable, unabridged, unacceptable, unacceptably, unaccommodating, unaccompanied, unaccountably, unaccounted, unaccustomed, unacknowledged, unadopted, unadulterated, unaffected, unaffordable, unafraid, unaided, unalloyed, unalterable, unaltered, unambiguous, unanimity, unanimous, unanimously, unannounced, unanswerable, unanswered,