A crossword was a word puzzle.

The Third Doctor worked on a crossword while Liz Shaw examined rock samples which purportedly came from Venus. (COMIC: Doctor Who and the Rocks from Venus) He was later thrown out of the Diogenes Club when his seventh incarnation showed him the answer to the crossword he was doing, causing the Doctor's earlier incarnation to shout at his older self and break the rules of silence. (PROSE: All-Consuming Fire)

At the time that the Seventh Doctor visited the library world of Catalog, crosswords were no longer known. (COMIC: Hunger from the Ends of Time!)

The Celestial Toymaker, disguised as an old man, worked on a crossword while in a duplicate Stockbridge, two of the answers being "Doctor" and "ensnared". (COMIC: Endgame)

During a contest to find the cleverest person to replace Rangorr, the Eleventh Doctor was able to escape while Rangorr was distracted by a crossword puzzle. (COMIC: The Cleverest King)

In June 1964, the Fourth Doctor did The Times crossword puzzle but he cheated by looking at the next day's issue. (AUDIO: Wave of Destruction)