Since the Amazon Prime adaptation of Neil Gaiman and Terry Pratchett's Good Omens launched at the end of May, global Google searches of the word 'ineffable' have gone through the roof. A coincidence, or some kind of divine plan? Who knows?
The term is used throughout the series, and clearly led to a number of viewers questioning their vocab library.
To save you having to search for it yourself and add to the trend, the dictionary definition of ineffable is “too great or extreme to be expressed or described in words”. Perhaps a reasonable description of the word’s rise in popularity!