Gasp with source of delight in range (7)
I believe the answer is:
breadth
'range' is the definition.
(I have seen 'Wide range ' mean 'breadth' so perhaps 'range' could also mean 'breadth')
'gasp with source of delight' is the wordplay.
'gasp' becomes 'breath' (I can't explain this - if you can you should give a lot more credence to this answer).
'with' means one lot of letters goes inside another.
'source of' says to take the initial letters (the start - or source - of the word).
The initial letter of 'delight' is 'd'.
'breath' enclosing 'd' is 'BREADTH'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for breadth that I've seen before include "Wide range" , "Wideness" , "Measurement from side to side" , "Liberality" , "Liberal view" .)