Big canine, last of eight by Welsh river (4)
I believe the answer is:
tusk
'big canine' is the definition.
'tusk' can be an answer for 'canine' (thesaurus). I am unsure of the 'big' bit.
'last of eight by welsh river' is the wordplay.
'last of' says to take the final letters.
'by' means one lot of letters go next to another.
'welsh river' becomes 'usk' (I've seen this before).
The last letter of 'eight' is 't'.
't'+'usk'='TUSK'
Can you help me to learn more?
(Other definitions for tusk that I've seen before include "Large tooth" , "Walrus's long tooth" , "Giant tooth" , "What's the point of a Jumbo that's hard" , "Elongated tooth" .)