Enter a clue or pattern or both:
The Clue
Ad-___ (improvises) (4 letter answer)
The Answer
LIBS
Tags
Notes
The answer LIBS is rarely seen, appearing only about once every 2100 puzzles.
Related Clues
Ad ___
Bldgs. for bibliophiles
The left, informally
Left-wingers
Some pols.
Some Cong. members