Q:

Does the word "coaxable" exist?

I started reading Stephen King's novel "Under the dome" and discovered the word coaxable:

Andy was an extremely coaxable man, and eventually Claudette had gotten her way.

I cannot find a definition for this word in the online dictionary.
I found a definition for the verb coax:

to influence or persuade (a person or animal) to do something by talking in a gentle and friendly way
to get (something) by talking in a gentle and friendly way

So my guess is that the author meant that Andy is easily coaxed by Claudette. 
Does this word exists or did the author invent it? If it exists, why is it not in the dictionary?
Is my understanding of the meaning correct?

A:

Your meaning of the word is correct.
The suffix

-able

is used to mean "something can be"

drinkable
can be drunk 
wearable
can be worn
coachable
can be coached

by extension

coaxable
can be coaxed
Horses are not very coaxable, thus the saying "You can lead a horse to water but you can't make him drink".
Children are usually coaxable with the promise of a present or a sweet, many parents might consider this tactic bribery.

