Look at this word. Read it. Try to say it. Ask yourself whether it’s five syllables – /kɛljuːzˈmætɪklɪ/ – or six – /kɛljuːzˈmætɪkəlɪ/ – or even seven – /kɛliuːzˈmætɪkəlɪ/. Decide, correctly, that it is most properly six but, honestly, if you’re ever going to say it, really five or at best five and a half (a long /l/ as in /kɛljuːzˈmætɪklːɪ/ is less than a syllable but more than not a syllable). Question whether your command of it will ever be such that you would use it. Wonder whether it will ever be imperative that you do so.
Wonder where this word comes from. Look it up, either in the Oxford English Dictionary or, if you don’t have that, right here in this article you’re reading right now. Find that it’s an Anglicization of Greek κελευσματικῶς plus the adverbial –ally ending. Find that that in turn comes from κελεύειν, which is a verb meaning ‘order’. Conclude that this is a fancy word meaning ‘as an imperative’ or ‘in the form of an imperative’ or just ‘imperatively’.
Muse. Ponder this word. Think about how it seems like keloid (a kind of cicatrix) and Kelita (a kind of singer), and decide that you would rather order up the latter than the former. Reflect further that it has a taste of charismatically, and decide that it would be helpful to be charismatic if you are going to be keleusmatic. Also not to be asthmatic.
Look in your wallet and wonder if you can afford this word, which is clearly not some stock five-dollar word. Wonder if it appears anywhere other than the OED, and chuckle as you think of it showing up in Urban Dictionary, that hotbed of crude slang and fourteen-year-old-boy definitions.
Find it in Urban Dictionary, complete with a definition that uses vulgarity.
Think about how it is odd to have such a long word referring to the imperative, which is generally by dint of circumstance a clipped form.
Use it anyway that one time you have a chance and remember it. Keep it on your lexical trinket shelf until then.