Exceptionally big hit by Queen in the 70s (6)
I believe the answer is:
bumper
'exceptionally big' is the definition.
'bumper' can be an answer for 'big' (I've seen this before). I am not sure about the 'exceptionally' bit.
'hit by queen in the 70s' is the wordplay.
I cannot quite see how this works, but
'hit' could be 'bump' (synonyms) and 'bump' is found within the answer.
'queen' could be 'er' (abbreviation for Elizabeth Regina) and 'er' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bumper that I've seen before include "kind of car" , "Protective vehicle bar" , "fender in US" , "It's a car fender in America" , "large drink" .)