Eastman (1881-1974) left England to go to Rarotonga as a missionary of the London Missionary Society (LMS) in 1913. In 1918 he was transferred to the Gilbert Islands (Kiribati) and was stationed at Beru. He was evacuated after the Japanese invasion in 1942 but returned to Beru in 1944.

Eastman says in an introduction to the dictionary that the words were collected 'partly as a means of obtaining a fluent use of the native language, and partly as a hobby'. On his transfer to the Gilbert Islands, he decided, at the request of European and Cook Islands friends, to publish his collection 'as far as completed'. The dictionary did not pretend to be a complete collection of all Cook Islands words, but most words of the Rarotongan language in ordinary use and many words of other Cook Islands dialects were included. It had been intended to publish the dictionary in New Zealand but because of a shortage of labour and material in 1918 this project was not carried out. Eastman said in a letter to the Pacific Manuscripts Bureau in 1973 that his work had formed the basis of Stephen Savage's 'A Dictionary of the Maori Language of Rarotonga', published by the Department of Island Territories, Wellington, in 1962.