Dog

Meaning
Loyalty, friendship, and steady presence. The Dog is a friend — someone reliable, familiar, and on the querent's side. It also stands for trust itself, and for the quality of dependability wherever it appears.
Its constancy is its whole meaning. A Dog does not surprise you.
The tone is warm and safe. It is one of the deck's most straightforwardly kind cards, and the tradition offers few cautions about it beyond the observation that loyalty can be given to someone who does not return it — which shows in the neighbours, not in the Dog.
Beside other cards
Often the subject when the question concerns a friend, and a modifier otherwise, where it makes its neighbour trustworthy or familiar. Dog + Letter is a message from a friend. Dog + Fox is loyalty being taken advantage of, and is worth reading carefully.