A word for "using two words next to each other that mean the same thing"?

I'm not even sure if there is a word for this. My partner says there is but I can't find it anywhere.

The example I'm giving is garlic aioli. The word aioli is a Mediterranean garlic and olive oil sauce, so why do they put garlic in front of the word aioli? It's like saying garlic, garlic and olive oil sauce.

Another example is Loch Ness lake, because apparently loch means lake in Scottish, it's like saying lake-Ness lake.

Anyways, I dunno if that makes much sense at all. Is there a word for that?

The word you want is pleonasm:

Pleonasm (/ˈpliːənæzəm/; from Greek πλεονασμός (pleonasmós), from πλέον (pleon), meaning "more, too much") is the use of more words or parts of words than are necessary or sufficient for clear expression: examples are black darkness, burning fire. Such redundancy is, by traditional rhetorical criteria, a manifestation of tautology. That being said, people may use a pleonasm for emphasis or because the phrase has already become established in a certain form.

A context-relevant excerpt from the article body:

Redundancies sometimes take the form of foreign words whose meaning is repeated in the context:

• "We went to the El Restaurante restaurant."
• "The La Brea tar pits are fascinating."
• "Roast beef served with au jus sauce."
• "Please R.S.V.P."
• "The Schwarzwald Forest is deep and dark."
• "The Drakensberg Mountains are in South Africa."

At chux's request, here are some examples without foreign phrases, courtesy of Mental Floss:

• Nape of the neck
• Gnashing of teeth
• False pretense
• Safe haven
• Bleary-eyed
• Veer off course

If the term is too technical for you, you could simply say that saying Loch Ness lake is redundant.

(Source: Wikipedia)

Tautology - Unnecessary repetition, usually in close proximity, of the same word, phrase, idea, argument, etc. The saying of the same thing twice in different words generally considered to be a fault of style (OED) although it can be used as a literary device.

Consider PIN...

"PIN number" is tautologous - it repeats "number" next to the initial N, which means "number".

"My PIN number that I use to identify my card with is on this piece of paper" - that I use to identify my card with is also tautologous.

When 'the same thing' is repeated in different languages (eg the examples in the OP) - Loch Ness Lake, La Brea Tar Pits, Drankensberg Mountains, Schwarzwald Forest - or, involves unfamiliar jargon - DVD disk, ISBN number - the tautology may not be redundant (superfluous, excessive; surplus; unnecessary (OED)), but in fact necessary for clarity (until such time as speaker and spoken-to can understand the unfamiliar language).

Tautology is a kind of pleonasm which is when more words are used in a sentence or clause than are necessary for clear expression (either as a fault of style, or as a rhetorical figure used for emphasis or clarity). For example,

Jill saw the building burning down with her own eyes. (She must have seen it with her own eyes).

The vote was completely and totally unanimous. (A unanimous vote cannot be anything but complete and total).

Although tautology and pleonasm are closely related, they are not synonyms. A tautology is a kind of pleonasm by definition. The reverse is not the case.

(Note that this answer refers to tautology in its original, rhetorical sense. In the early twentieth century philosophers Bertrand Russell and Ludwig Wittgenstein used the term tautology to describe a formula of the propositional calculus which is true under every assignment of truth or falsehood to its propositional letters, for example ‘If p and q then p’. In this context it is also used more widely to describe any proposition which is true because of its logical form rather than its content (OED)).