noun-modifying (irregular)
unexpected; unforeseen; unanticipated
Used prenominally to describe results, events, or situations that were not expected or predicted.
予期しない結果が出た。
An unexpected result came out.
予期しない出来事が起こった。
An unforeseen event occurred.
Compound of 予期 (yoki, 'expectation') + しない (shinai, negative form of する 'to do'), literally 'not expecting'.