Definition of "cuckow"

This employment was very irksome to him in every respect, […] Mr. Hector recollects his writing 'that the poet had described the dull sameness of his existence in these words, "Vitam continet una dies" (one day contains the whole of my life); that it was unvaried as the note of the cuckow; and that he did not know whether it was more disagreeable for him to teach, or the boys to learn, the grammar rules.'

1791, James Boswell, The Life of Samuel Johnson, LL.D.