Sentence:  Although Cecilia was the youngest of the surviving Thrale daughters, she had been the first to marry, <WSD>eloping</WSD> to Gretna Green in 1795 with John Meredith Mostyn of neighboring Llewesog Lodge. Both were underage. 
Meaning of the word marked with <WSD> tags:  To run away secretly for the purpose of getting married with one's intended spouse; to marry in a quick or private fashion, especially without a public period of engagement.