equation (ɪˈkweɪʒən, ʃən)  
—n  
1.  a mathematical statement that two expressions are equal: it is either an identity in which the variables can assume any value, or a conditional equation in which the variables have only certain values (roots) 
2.  the act of regarding as equal; equating 
3.  the act of making equal or balanced; equalization 
4.  a situation, esp one regarded as having a number of conflicting elements: what you want doesn't come into the equation 
5.  the state of being equal, equivalent, or equally balanced 
6.  a situation or problem in which a number of factors need to be considered 
7.  See chemical equation 
8.  astronomy See personal equation 
e'quational  
—adj  
e'quationally  
—adv 
equation e·qua·tion (ĭkwā'zhən, shən)
n.
A statement asserting the equality of two mathematical expressions, usually written as a linear array of symbols that are separated into left and right sides and are joined by an equal sign.
A representation of a chemical reaction, usually written as a linear array in which the symbols and quantities of the reactants are separated from those of the products by an equal sign, an arrow, or a set of opposing arrows.
equation (ĭkwā'zhən) Pronunciation Key

An expression of equality between two formulas in mathematics. The two formulas are written with an equal sign between them: 2 + 2 = 4 is an equation, as is E = mc2.