Beginning with A

Dictionaries make slow progress. Planning for the Oxford English Dictionary began in 1857; the last volume appeared in 1928. Slower still:

The Deccan College Post Graduate and Research Institute began work on a Sanskrit-to-English dictionary in 1948. The Royal Irish Academy began work on a historical dictionary of the Irish language, Foclóir na Nua-Ghaeilge [Dictionary of Modern Irish], in 1976. Neither project has made it through A (or in Sanskrit, अ).

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60 years later, Sanskrit dictionary stuck (Indian Express)
34 years compiling an Irish dictionary (The Irish Times)