The most common and most likely answer to this crossword clue is the 8 letter word SPRINGER
I've seen this crossword clue in The Times
S
P
R
I
N
G
E
R
More clues leading to the result SPRINGER
- Spaniel in season extremely eager
- Dog salivating, Pavlov starts with bell
- Vocalist keeping extremely popular type of spaniel
- Bounder‘s pet?
- Vocalist enlists pair that should raise game
- Spot not half, double the dog!
- Childless doppelgänger’s dog
- A jumping dog?
- Jerry’s spaniel
- At the start of a race, the odds double for dog
Buddy explains!

The straight part
We know that "Dog" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dog = springer.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SPRINGER mean?
SPRINGER noun- A person that springs.
- Anything that springs.
- A spring salmon.
- A stone at the base of an arch (from which the arch springs).
- A springing cow.
- A springer spaniel.
- A springbok.