There is a whole lot of analyzing going on in the oil and gas industry. If you are doing just one routine core test, you are doing an analysis (singular). If you are doing more than one, you are doing routine core analyses (plural). No, this is not a typo; it’s one of those funky plurals that doesn’t add an –s or –es to the end of the singular word. You certainly wouldn’t say “analysises.”
Another word that makes a plural by changing –sis to –ses is hypothesis. The plural would be hypotheses. Similarly, the singular “thesis” becomes the plural “theses.”
Which brings us to the question:
What is the plural of hippopotamus? Hippopotamuses or hippopotami?
“Both,” according to Webster.
“That depends,” according to the engineer. “Depends which one rhymes.”
“Neither,” according to the Grammar Geek. “Use hippos. The readers will know exactly what you mean.”