Definition: Occurring weekly.
The first usage of this word was in 1711 by Richard Steele in the Spectator, a magazine he had founded. It comes to us from the Greek word hebdomad which means a group of seven things or a period of seven days (hepta being Greek for seven). It changed to the Latin word hebdomadalis of the same meaning, and from there we have the English word hebdomadal.
Why this word?
Saying the word weekly is so prosaic, isn’t it? When something needs to be done on a weekly basis it is rarely an appealing task. Cleaning the house, taking out the trash, cleaning out cat litter, calculating billable hours for work- none of these are exciting tasks yet they are necessary. Wouldn’t it be nice to alleviate the boredom and tedium of these mundane chores by calling them something other than “weekly”? Class up that cat litter by changing it hebdomadally instead of weekly. Impress your parents by telling them you will take out the trash on a hebdomadal basis. The chores may be boring and routine but your vocabulary does not need to be.
How to use the word hebdomadal in a sentence?
“A little solace came at tea time, in the shape of a double ration of bread- a whole, instead of a half, slice- with the delicious addition of a small scrape of butter: it was the hebdomadal treat to which we all looked forward from Sabbath to Sabbath.”
Excerpt from Jane Eyre, provided by Google Books.