adj

• (dated) Firmly or securely fixed in place; stable.
  "That rope is dangerously loose. Make it fast!"
• (of people) Steadfast, with unwavering feeling. (Now mostly in set phrases like fast friend(s).)
  "I still hear you sayin', "Dear one, hold me fast""
• Moving with great speed, or capable of doing so; swift, rapid.
  "Plutonium-240 has a much higher fission cross-section for fast neutrons than for thermal neutrons."
• (computing, of a piece of hardware) Able to transfer data in a short period of time.
  "But at the microlevel it consists of an unimaginable number of atoms connected by springy chemical bonds, all jiggling around at a rate that even our fastest supercomputer might envy."

noun

• (British, rail transport) A train that calls at only some stations it passes between its origin and destination, typically just the principal stations.

intj

• (archery) Ellipsis of stand fast, a warning not to pass between the arrow and the target.

adv

• (of sleeping) Deeply or soundly .
  "The princess was sleeping fast, and her servants were fast asleep too."