spiral

Etymology

From Middle French spirale, from Medieval Latin spiralis, from Latin spira, from Ancient Greek σπείρα (speíra, “wreath, coil, twist”).

noun

1. (geometry) A curve that is the locus of a point that rotates about a fixed point while continuously increasing its distance from that point.
2. (informal) A helix.
3. A self-sustaining process with a lot of momentum involved, so it is difficult to accelerate or stop it at once.
   My beloved friends and family who sustained and grounded me as I fell into the rabbit hole of this project or down the spiral of new parenthood. 2015, Jane Ward, Not Gay, New York University Press, page xi
4. (rail transport) A section of track that forms a circle and crosses over itself, used for gaining height in mountainous territory.

adj

1. Helical, like a spiral.
   The formation of tornados and water-spouts is very probably identical with that of dust-storms and "devils," viz., a sudden disturbance of the vertical equilibrium of the atmosphere, where by an upward rush of air is generated, which rapidly becomes spiral. 1877, H. F. Blandford, Indian Meteorologist's Vade-mecum, page 140

verb

1. (intransitive) To move along the path of a spiral or helix.
   The falling leaves spiralled down from the tree.
2. (transitive) To cause something to spiral.
   You need to learn how to spiral a ball.
3. (figurative, intransitive) To increase continually.
   Her debts were spiralling out of control.