Did the Vulgar Latin verb "toccare" exist?

Question

According to the Royal Spanish Academy dictionary, the word tocar 'touch' has its origin in the toc toc onomatopoeia. Something similar is registered in Etymonline for the English verb touch:

from Old French tochier "to touch, hit, knock; mention, deal with" (11c., Modern French toucher), from Vulgar Latin *toccare "to knock, strike" as a bell (source also of Spanish tocar, Italian toccare), perhaps of imitative origin.

This source refers to a hypotetical verb toccare that existed in Vulgar Latin, that supposedly was the origin of our modern words. But I see that the word touch is translated into Classical Latin as palpo 'touch softly' (current Spanish: palpar) or tango 'touch' (origin of current Spanish tacto and tañer). So between these words and Old French tochier (11h century) or Spanish tocar (12th century) there must be a word that originated them.

So did the word toccare exist in Vulgar Latin as the origin of our current words for touch? If not, what could be transition from the Classical Latin words to the current ones?

Answer 1

As your question implies, the * in *toccare means that the word is unattested, i.e., there is no direct written evidence that the verb actually existed.

This does not mean that there is a good argument against its existence: vulgar Latin/Proto-Romance was the language of (mostly) illiterate people. It doesn't mean either that there is no good argument for its existence. The very fact that there are dictionary entries mentioning it means that at least some experts consider it likely enough.

Digging a bit deeper on the evidence for the existence of *toccare, the story goes like this:

(PIE¹) *dewk- (to draw, pull) > (PIE) *dukn- > (Proto-Germanic) *tukkōną (to pull, touch) > (Frankish) *tukkōn/tokkōn* (to touch) > (Latin) *tocco/-are

Part of the (extant, attested) evidence in which this genealogy is based is:

• (PIE) *dewk-: Latin dux, Spanish conducir (etc.)
• (Proto-Germanic) *tukkōną: English tuck, German zucken
• (Frankish) *tukkōn/ *tokkōn: Dutch tokkelen
• (Latin) well, you already mentioned it.

These reconstructions are based on the presence of the same root in one or several descendant languages. Moreover, the exact form of the unattested ancestor word is obtained by reversely applying the known sound changes that took place during the development of the descendant language.

The number of Romance languages with forms derived from *toccare is overwhelming, and all of them seem to point back at this particular form, hence the evidence for its existence is, IMHO, difficult to argue against.

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¹ Proto Indo-European language, from which all Indo-European family languages are hypothesized to come.

Answer 2

The wiktionary entry on the Italian verb toccare is somewhat more explicit, saying

Probably from a Vulgar Latin root *toccare, of Germanic or onomatopoetic origin. Compare French toucher, Friulian tocjâ, Portuguese tocar, Romanian toca, Romansh tutgar, Sicilian tuccari, Sardinian toccai, Spanish tocar, Venetian tocar

The existence of descendants in such many languages and the application of sound laws in the French descendant make us really confident that the verb toccare goes back to Vulgar Latin, but the asterisk before it tells us that it is a reconstruction and not attested in the corpus of preserved Vulgar Latin. How it entered Vulgar Latin is an open question, as far as I can see.