Other forms: sisters
Your sister is a girl or woman with the same parents as you. My older sister, two sisters, her sister-in-law.
Half-sister shares one parent and stepsister none. Sister is also a title for a nun and, in British hospitals, for a senior nurse in charge of a ward — a role rather than a family relationship. As an adjective it means paired or related: a sister company, a sister ship, a sister city. Note sisterhood; sisterly; and the informal use of sister as an address between women in solidarity.
1nounsisterA girl or woman with the same parents as you.~63%
“My sister and I share a bedroom, and we argue about everything.”
2nounnunA nun, or a senior nurse.~37%
“The sister on that ward has run it for eighteen years.”
Shares are an estimate: a language model read 13 sentences found in the wild and placed 8 of them on a sense (5 were unclear) — a count of our sample, not a measurement of English.
sister is a relative or title.
Old English sweostor was reinforced by Old Norse systir, which is why English has sister rather than the softer form the Old English word would have given. The Proto-Indo-European root survives everywhere: Latin soror, giving sorority, and Sanskrit svasar.
Middle English
suster
English, today
sister
From Middle English suster. a doublet of soror. Cognate with Scots sister, syster (“sister”), West Frisian sus, suster (“sister”), Dutch zuster (“sister”), German Schwester (“sister”), Norwegian Bokmål søster (“sister”), Norwegian Nynorsk - and Swedish syster (“sister”), Icelandic systir (“sister”), Gothic 𐍃𐍅𐌹𐍃𐍄𐌰𐍂 (“sister”), Latin soror (“sister”), Russian сестра́ (“sister”), Lithuanian sesuo (“sister”), Albanian vajzë (“girl, maiden”), Sanskrit स्वसृ (“sister”), Persian خواهر (“sister”). In standard English, the form with i is due to contamination with Old Norse systir (“sister”).
Etymology from Wiktionary, CC BY-SA