To devise self-satisfying but incorrect reasons for (one's behavior): “Many shoppers still rationalize luxury purchases as investments” (Janice Castro)
Mathematics To remove radicals, such as from a denominator, without changing the value of (an expression) or roots of (an equation).
Chiefly British To bring modern, efficient methods to (an industry, for example).
intransitive verb
To think in a rational or rationalistic way.
To devise self-satisfying but incorrect reasons for one's behavior.
derivatives
rátion·al·iźer
noun
The American Heritage® Dictionary of the English Language, Fourth Edition