or chiefly Brit  cae*si*um  n :  a silver-white soft ductile element of the alkali metal group that is the most electropositive element known and that is used esp. in photoelectric cells - symbol Cs - see ELEMENTtable   .
 
 
 
Similar sounding terms:  ses·a·me 
 
Published under license with Merriam-Webster, Incorporated.  © 1997-2024.