Thrust was, as the Fifth Doctor explained, "mass in motion". (TV: Castrovalva [+]Christopher H. Bidmead, Doctor Who season 19 (BBC1, 1982).) Thrust was generally produced by thrusters, such as those on a spacecraft. (TV: The Robots of Death [+]Chris Boucher, Doctor Who season 14 (BBC1, 1977). et al) Explosions could also produce upwards thrust. (TV: The Dalek Invasion of Earth [+]Terry Nation, Doctor Who season 2 (BBC1, 1964).)
Rocket thrust was, according to Tegan Jovanka, "enormous". It was so large that it enabled escape from gravity, such as that of Event One. Deleting rooms in a TARDIS using the architectural reconfiguration system could also produce large amounts of thrust. (TV: Castrovalva [+]Christopher H. Bidmead, Doctor Who season 19 (BBC1, 1982).)
According to the Thirteenth Doctor, positrons produced by the Tsuranga's particle accelerator interacted with the fuel materials to produce heat, which produced thrust. (TV: The Tsuranga Conundrum [+]Chris Chibnall, Doctor Who series 11 (BBC One, 2018).)
Other uses[]
A thrust could also refer to the use of a bladed weapon, such as a sword. (TV: The Masque of Mandragora [+]Louis Marks, Doctor Who season 14 (BBC1, 1976)., The Talons of Weng-Chiang [+]Robert Holmes, Doctor Who season 14 (BBC1, 1977).)
Brigadier Alistair Gordon Lethbridge-Stewart once referred to an Auton incursion as a "diversionary thrust". (TV: Terror of the Autons [+]Robert Holmes, Doctor Who season 8 (BBC1, 1971).)
The phrase 'thrust' was also a saying that meant to forcibly impose oneself on someone. (TV: The Chase [+]Terry Nation, Doctor Who season 2 (BBC1, 1965).)