### Clue: Having fun catching copper in barometer, perhaps (7)
### Answer: MERCURY 
 ### Explanation: Definition: in barometer, perhaps
 MERRY(having fun, resulting in being cheerful,merry) ***containing***o(catching) CU(the chemical symbol for copper).
Answer:  An allusive reference:  one finds mercury in a barometer, perhaps  as not all barometers use mercury to measure changes in atmospheric pressure.