caesium
noun /ˈsiːziəm/
/ˈsiːziəm/
(British English) (North American English cesium)
[uncountable] (symbol Cs)
- a chemical element. Caesium is a soft silver-white metal that reacts strongly in water, used in photoelectric cells.Word Originmid 19th cent.: from Latin caesius ‘greyish-blue’ (because it has characteristic lines in the blue part of the spectrum).