Solitario vs. solo

In Spanish, 'solitario' and 'solo' can both mean 'lonely' or 'solitary', but they are used in different contexts and have subtle differences in meaning.

Solitario

The word 'solitario' typically refers to something or someone characterized by solitude. It often describes a state of being where seclusion is inherent or preferred, and it can sometimes have a poetic or dramatic connotation.
Él vive en una casa solitaria entre las montañas.
(He lives in a solitary house among the mountains.)
La mujer solitaria paseaba por el parque vacío.
(The solitary woman walked through the empty park.)
El solitario faro estaba rodeado por el mar.
(The solitary lighthouse was surrounded by the sea.)

Solo

'Solo' can mean 'alone' or 'lonely', depending on the context. It often refers to someone who is by themselves physically rather than emotionally or intentionally. It can also describe actions performed without company.
Juan se siente solo en la ciudad nueva.
(Juan feels lonely in the new city.)
Ella decidió ir sola al cine.
(She decided to go to the movies alone.)
El niño juega solo en el patio.
(The child plays alone in the yard.)

Summary

'Solitario' and 'solo' both refer to being alone, but they differ contextually. 'Solitario' emphasizes solitude as a quality, often with a sense of intentional isolation or dramatic effect. In contrast, 'solo' generally denotes the physical state of being alone, without necessarily implying the emotional aspects of solitude.