90 was a number.
The Fourth Doctor told Romana that Time Lords had ninety lives, and that he had already gone through "about a hundred and thirty" of them. (TV: The Creature from the Pit)
According to a poster in a classroom at Deffry Vale High School, an acute angle was an angle of under 90°, while a right angle was an angle of precisely 90°. (TV: School Reunion)
The Tenth Doctor recalled that he visited the Medusa Cascade when he was "just a kid" of 90 years old. (TV: Turn Left)
Halcyon was 90 light-years from Earth. (AUDIO: The Resurrection of Mars)
In the Twelve Galaxies, 90 forvalars were equal to 1 krin. (TV: The Ghost Monument)
The Time Scaphe's initial flight was intended to spend ninety minutes in the Time Vortex and return ninety days into the future. (PROSE: Cat's Cradle: Time's Crucible)
The force 12 storm that caused the crash of the Elysium on 17 July 1888 blew up to ninety knots. (PROSE: Pride of Mayfield Star Lines Beached in Devastating Storm)