Boyd’s Bible Dictionary:

An unclean animal (Ex. 11:7; 22:31; Deut. 23:18); regarded with contempt (1 Sam. 17:43; 24:14; 2 Sam. 9:8; 2 Kings 8:13; Matt. 7:6; Rev. 22:15); guards (Isa. 56:10; Job 30:1); scavengers (1 Kings 14:11; 21:19-23; 22:38); enemies (Psa. 22:16-20).

Concise Bible Dictionary:

Constantly referred to in scripture as an unclean and debased animal: hence the unclean Gentiles or heathen are compared to dogs (Psa. 22:16; Psa. 59:6,14). The price of a dog was forbidden to be put into the Lord’s treasury, it was an abomination (Deut. 23:18). Hazael, a heathen, said, “Is thy servant a dog?” and the most offensive epithet was to call a man a dead dog. They were, and are, the scavengers of Eastern cities. All refuse is thrown into the streets and the dogs eat it. It was the dogs who ate the body of Jezebel, and licked up the blood of Naboth and of Ahab. In the New Testament it is the same: “without are dogs,” “beware of dogs,” used symbolically of those cut off and of the unclean: they return to their vomit again. The only apparent exception to the above is when the Lord compared the Syrophenician woman to a dog, and she said, “Yet the dogs eat of the crumbs which fall from their masters’ table.” In these passages the diminutive of the word is used, implying “little dogs, or puppies,” and these are often kept in houses until they grow up. But this does not remove the contempt implied in the term (Matt. 15:27). Wyclif translated “houndis” and “litil whelpis” in Mark 7:27- 28.

Strong’s Dictionary of Greek Words:

a primary word; a dog ("hound") (literally or figuratively)
KJV Usage: