The most common and most likely answer to this crossword clue is the 5 letter word UNUSE which also is the latest solution we found used in New York Times in 1983.
Why words become obsolete crossword clue answers
Here's a list of possible crossword answers ranked by the most likely to least likely.
| Answer | Likelyness | Letters | 
|---|---|---|
| UNUSE | 100 % | 5 | 
Words with a meaning similar to the clue: Why words become obsolete
These words may or may not be a possible solution to this crosswords clue.- what
 - bill
 - let
 - lets
 - letting
 - kopeck
 - homophony
 - superannuate
 - superannuated
 - dated
 - fossilize
 - assuage
 
Crossword Answer definitions
More crossword clues leading to the same solutions
Here's a few more crossword clues - all leading to the identical solution