======= By Longman =======
ensure = make sure
assure all other
assure = guarantee, ensure, insure, secure
Word origin for ASSURE
Date: 1300-1400
Language: Old French
Origin: assurer, from Medieval Latin assecurare, from Latin ad- 'to' + securus 'safe'
======= By WordNet =======
word ensure more widely
also equals to synonyms = guarantee, ensure, insure, assure, secure