My first source of aromatic resin (5)
I believe the answer is:
myrrh
'aromatic resin' is the definition.
(I've seen this before)
'my first source' is the wordplay.
I cannot quite see how this works, but
'my' is found in the answer.
This explanation may well be incorrect...
'of' is the link.
Can you help me to learn more?
(Other definitions for myrrh that I've seen before include "Bitter tree gum, used in perfume and incense" , "Wise Men's gift" , "One of the first ever Christmas presents" , "One of the 'three gifts'" , "fragrant substance" .)