Ngrams shows "hiccough" was 5-6x more common than "hiccup" between the 1860s and 1920s. https://books.google.com/ngrams/graph?content=hiccough%2Chiccup&year_sta

Ngrams shows "hiccough" was 5-6x more common than "hiccup" between the 1860s and 1920s. https://books.google.com/ngrams/graph?content=hiccough%2Chiccup&year_start=1800&year_end=2019&corpus=en-2019&smoothing=3 https://books.google.com/ngrams/graph?content=hiccough%2Chic... . An archive.org search found plenty of texts from that era using hiccough, though often with some hiccups as well. This one from 1886 is interesting: https://archive.org/details/b21699331/page/n1/mode/2up?q=hiccough+hiccup https://archive.org/details/b21699331/page/n1/mode/2up?q=hic... > No doubt many of my professional brethren are well acquainted with the Hippocratic aphorism <Greek transcription omitted> "Sneezing occurring after hiccough removes the hiccough,” or, as it is rendered by Adams, “Sneezing coming on, in the case of a person afflicted with hiccup, removes the hiccup.” The 1886 author uses hiccough while quoting the older Adams reference, from 1849, as using hiccup (primary reference for Adams is at https://archive.org/details/genuineworksofhi02hippuoft/page/754/mode/2up?q=hiccup https://archive.org/details/genuineworksofhi02hippuoft/page/... )