Morve vs. mucus
In French, the distinction between these terms relies heavily on the level of formality and the context in which they are used. While morve is colloquial and synonymous with the English snot, mucus is the technical and polite term corresponding to mucus.
Morve
B2This is the informal, colloquial, and sometimes slightly vulgar word for nasal discharge. It corresponds directly to snot in English and is often associated with being messy, childish, or gross.
Le bébé a de la morve qui coule du nez.
(The baby has snot running from his nose.)
Va chercher un mouchoir, tu as de la morve sur la joue.
(Go get a tissue, you have snot on your cheek.)
C'est dégoûtant, il mange sa morve !
(It is disgusting, he is eating his snot!)
J'ai éternué et j'ai mis de la morve sur ma manche.
(I sneezed and got snot on my sleeve.)
Mucus
C1This is the formal, scientific, and medical term used to describe the substance. It is used in biological contexts, at the doctor's office, or when trying to be polite, corresponding to the English word mucus.
Ce sirop aide à fluidifier le mucus dans les poumons.
(This syrup helps thin the mucus in the lungs.)
Le médecin a dit que l'excès de mucus est dû à une allergie.
(The doctor said that the excess mucus is due to an allergy.)
Le mucus nasal piège la poussière et les bactéries.
(Nasal mucus traps dust and bacteria.)
Les escargots laissent une trace de mucus derrière eux.
(Snails leave a trail of mucus behind them.)
Summary
Use morve when speaking casually about a runny nose, usually implying a mess or snot. Use mucus in medical, scientific, or polite conversations when referring to the biological substance.