First used by the novelist Marie Corelli for the heroine of her novel Thelma (1887). She was supposed to be Norwegian, but it is not a traditional Scandinavian name. Greek thelēma (neuter) means ‘wish’ or ‘(act of) will’, and the name could perhaps be interpreted as a contracted form of this.
English: topographic name for someone who lived on a slope, from Middle English side ‘slope’ (Old English sīde), or a habitational name from Syde in Gloucestershire, named with this word. This name is also established in Ireland.