The English translation of the expression warme Schwester is “warm sister” and is a little used slang to refer to lesbians that has its origin in the expression warme Bruder, whose literal translation is “warm brother” and which is a derogatory expression used against homosexual men especially in the past.
As warme Schwester, other “warme” (warm) expressions also used infrequently to attack lesbians are warme Schwesternorden (Order of warm sister), warme Stute (warm mare), warme Pro (warm professional = lesbian prostitute), and warmer Ratz (warm rat) or warmer Wetsch to name a lesbian prison officer (Wetsch could be an expression of Rotwelsch related to the police). But not all “warm” expressions are derogatory since warme is also used positively inside and outside the LGBT community. As an example, the expression Warmherzig (warm heart), used as a synonym for gay and lesbian.
In addition, there is another series of expressions pertaining to the Rotwelsch jargon and to the slums of the cities that are difficult to translate and interpret as they are worme Stuatn (warm mare), warmer Chomes and warme Fladern (hot thief), warme Hebn, warme Schanettl (warm Jane), warmes Röhrl and warme Tschesa.
The relationship of warmth with lesbianism is none other than extending the insults against gays to lesbians. For this reason, we recommend you to read the entries “warme Bruder” and “warme” in our German Gay Dictionary.