The word diaper was first used in a story about a knight from the year 1350, when it was spelled diapre. After that, it also took the forms ​dyapre, dyapere, dyaper, dyoper, dieper, dyeper, diapre, and dipar until diaper became the standard during the seventeenth century. The term comes from the Old French word diapre, which specifically referred to a a type of cloth with a repeating pattern (these were often used as diapers). That, through Latin diasprum, traces to the Ancient Greek word diaspros, which was composed of the prefix dia-, meaning "across" or "thoroughly, and the root aspros, "white" (the diapres were typically white). Dia derives from Proto-Indo-European dwo ("two") and aspros was relatively rare but is thought to also be from PIE. The British slang word nappy is a diminutive of napkin.

The words orthodontics and orthodontist were both modelled after orthodontia, which was created in 1849 from the Greek word orthos, meaning "straight", odon, meaning "tooth", and the noun-forming suffix -ia. Orthos, the root in words like orthopedic and orthography​, comes (through Proto-Hellenic ortwos) from the Proto-Indo-European root herd, meaning "upright". Odon (the origin of the second part of the word mastodon) traces, through Proto-Hellenic odonts, to Proto-Indo-European hdonts, which still meant "tooth". Herd is also the etymon of English arduous, and hdonts of English tooth. After being popularized around the turn of the twentieth century, usage of the word orthodontia peaked in the early 1920s and late 1930s, and has been decreasing since due to being overtaken by orthodontics.

The word eclair​ was first used in an 1861 issue of Vanity Fair, when it was borrowed directly from a French word meaning "lightning". It was named that because the dessert was meant to be eaten quickly, and that word comes from Old French esclair, which could be defined as "daylight" or "flash of light". That traces to the Latin verb exclarare, which translates to "illuminate" and was composed of the prefix ex-, meaning "out" (and, as we've seen before, tracing to Proto-Indo-European eghs, also "out") and the root clarus, meaning "clear". Clarus, the etymon of words like declare, clarinet, and Claire, derives from the Proto-Indo-European reconstruction kelh, which meant "call". Since the turn of the century, usage of eclair with an acute accent over the e has been increasing while the variation with no accent has been decreasing. Probably an attempt to make the food seem fancier.

The commonly accepted plural for corgi is corgis, but if we're to be etymologically accurate, it should be corgwn. This reflects the word's origin; it was borrowed in 1921 from Welsh corci. That was a compound of the words cor, meaning "dwarf", and ci, meaning "dog". Cor traces to the Proto-Brythonic word korr, which is from Proto-Celtic korros ("stunted")  and ultimately Proto-Indo-European. Ci, which was pronounced like "key" (the velar stop was voiced after the r) and comes from Proto-Brythonic ki and Proto-Celtic ku, which had the same definition but could also mean "wolf". Finally, that's reconstructed to the Proto-Indo-European root kwon. The term corgi has been increasing in literary usage over time, peaking in the year 1999, and according to Google Trends it's most searched for in Wyoming.

The word calendar was first used in 1275, when it was spelled as kalender. Other alternations included kaluneder, kalendere, kalandar, and calandar until calendar was standardized during the eighteenth century. Through Old French, that traces to the Latin word kalendarium (sometimes calendarium), which meant "account book" and was associated with months because it was named after the kalandae (or calendae), the first day of the Roman month. This is because all debts were due during that time. Kalandae derives from the reconstructed Proto-Indo-European word kele, which meant "shout" because, at the start of the calends, priests were supposed to go around shouting that it was a new month and how long it was to the nones (the next part of the month). Usage of the word calendar over time has been steadily increasing over time, reaching its highest point so far in the year 2001.

This is a bit of an unorthodox post, but I recently wrote a paper critiquing Stephen Bax's analysis of the language in the Voynich manuscript, and I just wanted to post it here on my site for posterity.