/soʊl/
[adjective] Being the only one; not shared with anyone else. For example, you might be the sole owner of something if no one else owns it with you.
'Sole' comes from a Latin word meaning 'alone' — the same root that gave us the word 'solo' and even 'solitary confinement'.
The word 'sole' in its sense of 'only' or 'single' travels to us from the Latin word 'solus', meaning 'alone' or 'by oneself'. This was a common and versatile word in classical Latin, used to describe anything that stood apart from others — a single person, a lone object, an unshared claim. It carried a quiet dignity, the sense not merely of loneliness but of singular distinction.
From Latin 'solus', the word passed into Old French as 'soul' or 'seul', meaning 'alone' or 'only'. This French form was picked up by English speakers in the 14th century, during the long period following the Norman Conquest when French was deeply woven into the fabric of English vocabulary. English adopted the spelling 'sole' and settled on it as a clean, single-syllable adjective that could describe exclusive ownership, unique status, or a person standing entirely alone in a role.
The Latin root 'solus' is remarkably productive in English, having sent several distinct descendants into the language through different routes. Italian preserved it as 'solo', which English borrowed directly in the 17th century to describe a musical performance by one person alone — giving us the concert hall 'solo'. The same root also gave English 'solitary' (via Latin 'solitarius') and 'solitude' (via Latin 'solitudo'), both arriving through Old French or directly from Latin in the 14th and 15th centuries. Even 'sullen', surprisingly, has been linked by some scholars to this cluster, though its path is debated.
Interestingly, English has two other completely unrelated words spelled 'sole'. One is the bottom of a shoe or a foot, which comes from Latin 'solea' meaning a sandal or the flat bottom surface — itself related to 'solum', meaning ground or floor. The other is the flatfish called a sole, named for the same reason: its flat, ground-hugging shape. These three 'soles' — the adjective meaning only, the noun meaning the underside of a shoe, and the fish — are homonyms that happen to share a spelling but come from different Latin ancestors.
Over the centuries, 'sole' the adjective has remained remarkably stable in meaning. It still means exactly what it meant when English first borrowed it: one and only, belonging entirely to one person or thing, without division or exception. You are the sole heir, the sole survivor, the sole reason. In an age when so many English words have drifted far from their origins, 'sole' carries its original Latin meaning intact — alone, then as now.