Definition of yellow dog:
(n) :
(US, informal) An item or person of low value.
(n) :
(US, especially Southern US) A Carolina dog.
(n) :
Used other than figuratively or idiomatically: see yellow, dog.
(n) :
(US politics, uncommon) Ellipsis of Yellow Dog Democrat. [(US politics, dated) A Democrat, especially a Southern one, who votes a straight party ticket; one who invariably votes for Democratic candidates.]
(n) :
Alternative letter-case form of yellow dog, chiefly used when the word has the sense "Carolina dog" or the sense "Yellow Dog Democrat". [Used other than figuratively or idiomatically: see yellow, dog.]