ERSTWHILE meaning : 1. previous 2. previous. Learn more. 2 meanings: 1. former; one-time 2. archaic long ago; formerly.... Click for more definitions. Have you ever come across the word erstwhile meaning in your reading and wondered what it means? You’re not alone! This beautiful English word carries a sense of nostalgia and history that many people find intriguing. Today, we’ll explore the erstwhile meaning in depth, making it easy for students, professionals, and curious minds to understand and use this word confidently. Definition of erstwhile adjective in Oxford Advanced Learner's Dictionary. Meaning , pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.