Just a flowery word for day.
The Livelong Day - 2008 was released on: USA: 1 May 2008 (PDX Film Festival)
NCIS Los Angeles - 2009 The Livelong Day 5-7 is rated/received certificates of: USA:TV-14
NCIS Los Angeles - 2009 The Livelong Day 5-7 was released on: USA: 5 November 2013 Germany: 16 February 2014
It's not an idiom. It means just what it says -- it's either going to rain that day, or it will be sunny.
It takes a long time to do an important job
It refers to a day being noteworthy or of hanging a banner of announcement, usually of good news.
"A black day" is an idiom in contemporary English that is relatively uncommon but still quite useful. With "black" referring primarily to darkness (of night, of a storm, etc.) when there ought to be light, its basic meaning is simply this: "a bad or difficult day."
RFP is not an idiom. It's an abbreviation.
It's not really an idiom. It means "what are you thinking about."
It is not an idiom, it means your nose is itching.
The phrase means to be nervous or anxious about something.
idiom means expression like a page in a book