"English-Esperanto Dictionary" by J. C. O'Connor and C. F. Hayes is a language reference work written in the early 20th century. The book serves as a comprehensive bilingual dictionary that translates English words into their Esperanto equivalents, catering particularly to students and enthusiasts of the Esperanto language. It aims to facilitate communication and understanding for English speakers learning Esperanto and vice versa. The opening portion of the dictionary introduces the work's purpose, acknowledging the high demand for such a resource as it is the first of its kind. The authors explain the various linguistic features of Esperanto, including the importance of roots, prefixes, and suffixes, which help in forming new words. They include a preface that highlights the challenges faced while compiling the dictionary and express gratitude for the support received from prominent figures in the Esperanto community, setting the stage for a user-friendly reference tool for language learners. (This is an automatically generated summary.)