青天 (せいてん, seiten) Japanese meaning: blue sky | KotomoraFreq.FrequencyTop 100,000 Expressions
青天の霹靂a bolt out of the blue; a sudden and surprising event
clear weather; blue sky and bright sun · cleared of charges; proven innocent; clear conscience
Etymology
Compound of 青 (blue) and 天 (sky, heavens). The reading せいてん is the on'yomi for both characters.