All-time low is a term used to describe the lowest point of something. The crossword solutions for this term are NADIR (5 letters), ATAN (4 letters), and ROCKBOTTOM (10 letters). NADIR is an Arabic word meaning 'the lowest point' and is often used in astronomy to refer to the point on the celestial sphere directly opposite the zenith. ATAN is an acronym for 'arctangent', which is a mathematical function that calculates the angle between two points. Finally, ROCKBOTTOM is a phrase that is used to describe the absolute lowest point of something.