And Bruce Griffiths, whose 1,800-page, 210,000-word work will cost pounds 40 when published, says that if he had his time all over again, he would never have started it.
"If I'd known back in 1975 what it was going to involve, I certainly never would have started. Life is too short to spend on something like this," said Dr Griffiths of the University of Wales, Bangor.
But the dictionary will be a milestone for the Welsh language, which declined dramatically between 1931 and 1981 from 908,000 speakers to 508,000, but is now showing signs of a revival.
As well as giving Welsh equivalents for thousands of English words, the dictionary provides, for the first time, Welsh equivalents of common English phrases. In many cases a banal English phrase has a far more colourful Welsh translation.
The Welsh for "to give up", for example, is rhoi'r ffidd yn y to, which literally translated means "to hang the violin in the roof". In the same way, when the weather is wet the Welsh use a phrase meaning: "It's raining old women and sticks."
"To attain a goal" becomes "to take the stone to the wall", while the Welsh for "he was out of breath" is "he arrived with his wind in his fist". "To change the subject" is "to turn the cat in the pan" and "to go bust" is "the sow has gone through the shop".
Some Welsh words differ little from the English: "ahoy" becomes ahoi; "balloon", balwn; and "disco", disgo. Newer words have had mixed fates: the Welsh for "Aids" is Aid, and Dr Griffiths' suggested translation for "Internet" is Rhwydwaith.
Free at last of his burden, Mr Griffiths has made his plans. "What am I going to do? Take it easy and wait for the money to flow in and be sent to my retirement home in the South of France."Reuse content