An archaic or alternative spelling of 'gulf,' meaning a large area of sea or ocean that cuts into the land.
From Old French 'golfe,' from Italian 'golfo,' from Greek 'kolpos' meaning bosom or bay; the 'ph' spelling is an older English variant influenced by Latin spelling conventions.
The spelling 'gulph' shows how English spelling was inconsistent and influenced by classical languages—people would add 'ph' to look more educated, even when it didn't match pronunciation, which is why we still see 'ph' in words like 'phone' and 'graph' today.
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