If you look at the Online Etymology Dictionary (which is quite good), you get the following statement regarding the term “dog”

dog (n.)

“quadruped of the genus Canis,” Old English docga, a late, rare word, used in at least one Middle English source in reference specifically to a powerful breed of canine; other early Middle English uses tend to be depreciatory or abusive. Its origin remains one of the great mysteries of English etymology.

The word forced out Old English hund (the general Germanic and Indo-European word, from root from PIE root *kwon-) by 16c. and subsequently was picked up in many continental languages (French dogue (16c.), Danish dogge, German Dogge (16c.)). The common Spanish word for “dog,” perro, also is a mystery word of unknown origin, perhaps from Iberian. A group of Slavic “dog” words (Old Church Slavonic pisu, Polish pies, Serbo-Croatian pas) likewise is of unknown origin. 

---

Germanic and Latin mystery words are not currently within the investigatory purview of this site. Things, however, look different for Suavic words. The word pies meaning “dog” is attested in Polish from the XIVth  century. Other Suavic languages have similar terms for dog (Czech pes, Russian pës, the above mentioned Serbo-Croatian pas or, for that matter, the (East) German Petze). These are derived, perhaps, from the proto-Suavic *pьsъ.

Now, as noted above, this Suavic mystery word is different and, apparently, not derived from the reconstructed PIE version *kwnto-, itself a “dental enlargement” of the root *kwon- “dog. I will get back to that last root at the end of this post but, in the meantime, let’s see what canine words are derived by modern etymological arts from *kwon-:

• canis (Latin)
• cão (Portuguese)
• šuo (Lithuanian)
• Hund, hound, *hundaz (German, English, Proto-Germanic)

And, of course, others.

But what about our *pьsъ? Where does it come from? The word is supposedly a Suavic innovation with no obvious parallels in other IE languages. That said a number of theories exist, with most trying to establish some IE connection. Here are some of them.

pecus

Aleksander Brückner was noncommittal suggesting that “they” derive the word from the IE (“Arian”) word for “cattle” which had been retained in some IE languages (Latin pecus but there are also, apparently, equivalents in Old Indian). Perhaps because Suavs could not tell the difference between a cow and a dog or perhaps the latter was used to guard cattle.

ps, ps! 

More recently, Wiesław Boryś prefers to derive it from the words used to lure dogs which, apparently, were ps, ps!  i don’t know if this was ever attested but the Polish Dialects Dictionary does list this method of luring hounds. Also, some Poles apparently used the scream psa! as part of hallooing.

specie

Another theory derives this word from something like the Latin specie. This means something like “I see, observe.” This would place the Suavic dog into his familiar “pastoral,” “sheep dog” vocation. Or perhaps it would establish the same as man’s “guardian” and “protector.” Take your pick.

pstry

Julius Pokorny connected pies with the Proto-Suavic *pьstrъ meaning “colorful” multi-colored. For example, in Polish you have pstry. This is cognate with the Suavic pisać meaning to write but previously to paint (in colors presumably). For example, we have the pisanka as the word for “Easter egg”. Whether this is also cognate with pstrąg, the Polish word for “trout,“ I don’t know. Perhaps we can connect all to pisces and conclude that Suavs painted (and wrote) with fish oil, blood or innards.

Does this mean that Suavs only had mutt or spotted dogs?

Or does it mean that Suavic dogs were into painting?

pissing

Another version of this word connects this to, well, the act of urination which, apparently, is to have a similar root as the Suavic *pьsati, “to write” but originally “to paint”. Obviously, a dog tends to urinate in quite a visible fashion – at least a dog that one spends some time around. Perhaps, Suavs did not have a name for a dog until the animal became domesticated (which given the timeframes of canine domestication and development of PIE, is, presumably, a truism). 

Apparently, this sheds some light on how the early Suavs first painted…

sheep

Another PIE theory connects the Suavic pies with a hypothetical *pheḱhu- which referred originally to “sheep”.

If you read Polish, you can get more data on these theories here.

---

This is all well and good but is there another possibility?

A suggestion is offered by Brückner’s dictionary under the heading piechota. The word today means “infantry” but its original meaning is rather broader. It refers specifically to the act of walking. Brückner makes the following statement:

“piechota… the almost [yes!] only remainder among Suavs of the urword for “leg”: Ind. pad-, Greek pūs, podos, Latin. pēs, pedis, German Fuss (Gothic fōtus)…”

As you can see above, terms for “feet” and “legs” were sometimes used interchangeably at least over time.

What is the first thing (or things) that you associate (physically) with a dog? I submit its legsm feet or paws.

In fact, we, to this day, commonly describe dogs as our “four legged friends.”

And do you know what you get when you translate “feet” into:

• Italian? > piedi
• French? > pés
• Galician? > pés
• Portuguese? > pés
• Spanish? > pies

The “s” ending, of course, denotes the plural but the “plural” begs to be addressed when you look at a dog since a dog, quite visibly utilizes twice as many appendages to move around as a human does. Of course, so do horse, donkeys, elephants and an infinite number of other animals but only dogs lay the claim to being man’s best friend and, thus, it is the dogs’ difference from their human companions that received the most attention from the latter (as demonstrated by the above saying).

So what does this mean? To my mind, it means that there is a component of Suavic that suggests a very early contact with a population to whom the word pies would have meant as much as it does to this day’s Spaniards and Portuguese. Perhaps, this is a Venetic contribution.

Now a few other interesting things:

• the PIE root for “dog” – *kwon- – surely has to have a connection to the Suavic word for “horse” – koń. And yet Brückner insists that there must have been a consonant between the o and the ń. Unlikely, I think the answer is right here.
• slightly in jest, do you know what the Portuguese word is for a “puppy”? It’s cachorro. It remains to be seen whether this can be connected to the Suavic kaczor – meaning “male duck” (or if you want to be proper about it and to relate this somehow to dragons, a “drake”).

In summary, the ancient Suavs applied the PIE word for “dog” to their horses, seem to have gotten their word for dog from some Latin-related word denoting “feet” and kept duckling drakes as their puppies. Got all that?