### Clue: A firm on St Lucia working without electricity? (10)
### Answer: ACOUSTICAL 
 ### Explanation: Definition: without electricity
 A + CO(abbrev. for "company", a commercial firm) **placed above**(on, in a down clue) **anagram of**(… working) ST LUCIA.
Defn: .., when referring to a musical instrument that does not produce nor enhance sound electrically, commonly applied to a non-electric guitar.