Bank holiday and Red-letter day

Bank holiday noun - Any of several weekdays when banks are closed; a legal holiday in Britain.

Red-letter day and bank holiday are semantically related. In some cases you can use "Red-letter day" instead a noun phrase "Bank holiday".

Red-letter day noun - A memorably happy or noteworthy day (from the custom of marking holy days in red on church calendars).

Bank holiday and red-letter day are semantically related. You can use "Bank holiday" instead a noun phrase "Red-letter day".