### Clue: FTSE in collapse all about, so working at once (8)
### Answer: EFTSOONS 
 ### Explanation: Definition: at once
  **Anagram of**(collapse) FTSE **containing**(all about) [SO + ON(working, as with an appliance that's switched on). 
Answer: Archaic and arcane word, new to me, meaning soon after, or, at a stretch, at once.