to attribute (e.g. one's actions) to rational and creditable motives, without analysis of true, esp unconscious, motives, in order to provide plausible reasons for conduct

Mankind has a powerful need to rationalize its actions — Enoch Powell

to increase the efficiency of (e.g. an industry) by more effective organization, usu entailing reductions in the workforce

to free (a mathematical expression) from parts that are irrational numbers

to provide plausible reasons for one's actions, opinions, etc

His ability to rationalise verged on the psycopathic — Guardian