Abarim Publications' online Biblical Greek Dictionary
The noun λυκος (lukos) means wolf, and in the classical world, the wolf did not have the romantically high standing as it does in our culture. The Latin word for wolf is lupus, which in turn is thought to derive from the Greek λυπη, lupe, meaning sorrow. Hence, to the classics the wolf was a sorrowful one: a howler, or rather: whiner.
It has always been common knowledge that wolves were related to dogs, and dogs had a very low status (see our article on כלב, kaleb meaning dog). But where dogs could be expected to do some labor or guard a premise, wolves were seen as self-pitying and cowardly sneak thieves who preyed upon the defenseless (Ezekiel 22:27), and besides take some for food (all creature have to eat, so that's no reason to criticize), they also terrified and scattered the rest (John 10:12, Acts 20:29).
Calling someone a ravenous wolf (Genesis 49:27) was a dire insult. In Greece, molesters of children were called wolves, and Jesus called false prophets wolves dressed in sheep's clothing (Matthew 7:15).