Lively sextet with lead bass sound off (7)
I believe the answer is:
vibrant
'lively' is the definition.
(I've seen this before)
'sextet with lead bass sound off' is the wordplay.
'sextet' becomes 'vi' (group of six - VI are the Roman numerals for six).
'with' means one lot of letters go next to another.
'lead bass' becomes 'b' (I can't explain this - if you can you should give a lot more credence to this answer).
'sound off' becomes 'rant' (to sound off is to rant or complain).
'vi'+'b'+'rant'='VIBRANT'
Can you help me to learn more?
(Other definitions for vibrant that I've seen before include "Dynamic" , "Bright, thrilling or resonant" , "Strong and vivid" , "Full of energy, lively" , "Brightly-coloured" .)