Seul vs. solitaire
The French words seul and solitaire both relate to the concept of being alone, yet they are used in somewhat different contexts and convey different nuances in French.
Seul
A2Seul generally means alone and can refer to both physical and emotional states of solitude. It is often used to describe someone who is physically by themselves or something that is singular or unique.
Elle mange seul à la cantine.
(She eats alone in the cafeteria.)
C'est le seul exemplaire du livre.
(It's the only copy of the book.)
Il se sent seul même dans la foule.
(He feels alone even in a crowd.)
Solitaire
B1Solitaire also means alone, but it often carries a connotation of emotional isolation or a preference for avoiding the company of others. It can be used for people who enjoy being alone or animals living isolated from others of their species.
Il préfère vivre en homme solitaire.
(He prefers to live as a solitary man.)
Le loup solitaire s'éloigne de la meute.
(The lone wolf strays from the pack.)
Elle a choisi une vie solitaire dans la montagne.
(She chose a solitary life in the mountain.)
Summary
Seul is more general and widely applicable, relating to the state of being alone, while solitaire has a more specific usage emphasizing emotional solitude or deliberate isolation. Understanding these subtleties is important for accurate and expressive communication in French.