"Lingua" is not an English word.
To my knowledge it is only found (in English) in the expression lingua franca which comes from Italian and refers to a "common language" between two or more groups of people.
It is a loan word .
When referring to the anatomical thing, we always say "tongue" and never "lingua."
"Lingua" itself is Latin, and this root is the basis for several English words like "language," "linguistics," "bilingual"; as well as scientific names in anatomy like "lingual artery."
ell.stackexchange.com/users/82065/TypeIA
lingua isn't used on its own, but the latin root is part of a lot of words.
sublingual - below the tongue linguist - someone who studies languages bilingual - someone who speaks 2 languages linguine (or linguini) -
a delicious pasta, that somehow relates to tongues.
ell.stackexchange.com/users/104590/Grady Player
The simple explanation is that in anatomy, latin terms are used (for adjectives "dorsal"= of the back, "ventral"= of the belly/front, "jugular"=of the throat, "ischemic", "sciatic", "cranial", ... ; or for parts, like "retina", "vena cava", "atrium", "vestibula", "cranium", ... ).
In English, you will find "lingua"/"lingual" almost exclusively used in an anatomy context, because there it's "proper".
One of the advantages of using Latin is that a first year's med (or bio) student starts from a blank slate (I'd say, tabula rasa ):
There's no imprecise, overlapping terminology, no confusing half-synonyms (no "tummy", "belly", "stomach" for generally the same region).
The other advantage is that (as lingua franca in classical learning) older & foreign language texts use exactly the same verbs and adjectives; important as much scientific research is published in English but not written nor read by native speakers.
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I cannot think of any use of lingua however sublingual means under the tongue.
Sub means under or below and lingual means tongue.
The word tongue is not used for the anatomical structure alone.
For instance, the tongue of the shoe.
ell.stackexchange.com/users/104585/BillyBob 63
The noun lingua is not used (Is it even in an English dictionary?).
It's probably been made redundant in the formation of the English language from its ancestors.
Tongue is always used as the noun, and can mean "language" as well, for example mother tongue (the language one learned from one's mother).
On the other hand, the adjectival form lingual is used, meaning "related to the tongue".
Not common on its own.
Prefixed forms are more common, and can relate to both meanings.
Sublingual : under the tongue.
Bilingual : fluent in two languages.
ell.stackexchange.com/users/24547/nigel222
Dictionary.com definitions:   tongue  - the usually movable organ in the floor of the mouth in humans and most vertebrates, functioning in eating, in tasting, and, in humans, in speaking.     lingua  - the tongue or a part like a tongue   Both words have the same meaning.  Why is the word "lingua" almost not used in spoken language? And in what cases can the word lingua be used?
What's the difference between words "tongue" and "lingua"?
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<meaning><word-usage><difference>
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ell.stackexchange.com/users/104550/Mikhail
To my knowledge it is only found (in English) in the expression  lingua franca  which comes from Italian and refers to a "common language" between two or more groups of people. "Lingua" itself is Latin, and this root is the basis for several English words like "language," "linguistics," "bilingual"; as well as scientific names in anatomy like "lingual artery." Tongue  is always used as the noun, and can mean "language" as well, for example  mother tongue  (the language one learned from one's mother “Lingua" is a medical term from Italian and "tongue" is the preferred everyday term.
“Lingua" is a medical term from Italian and "tongue" is the preferred everyday term.