A saint whose day is traditionally celebrated during a spell of cold weather (chiefly in plural); specifically (in continental Europe) any one of the saints whose days fall within a short period in May traditionally believed to be liable to frost.
Origin
Late 19th century.
Definition of ice saint in US English:
ice saint
noun
A saint whose day is traditionally celebrated during a spell of cold weather (chiefly in plural); specifically (in continental Europe) any one of the saints whose days fall within a short period in May traditionally believed to be liable to frost.