Might it be that sister? Poor nun in trouble!

Wiktionary Word definitions in Wiktionary
n. (context grammar English) A pronoun that introduces a relative clause and refers to an antecedent. Some words that can be used as interrogative pronouns can alternatively be used as relative pronouns: ''what'', ''which'', ''who'', ''whom'', and ''whose''. ...

Wikipedia Word definitions in Wikipedia
A relative pronoun marks a relative clause ; it has the same referent in the main clause of a sentence that the relative modifies. An example is the English word which in the sentence "This is the house which Jack built." Here the relative pronoun which ...

Longman Dictionary of Contemporary English Word definitions in Longman Dictionary of Contemporary English
noun EXAMPLES FROM CORPUS ▪ The most notable is the relative pronoun that, which can only be used with a restrictive relative clause.

WordNet Word definitions in WordNet
n. a pronoun (as `that' or `which' or `who') that introduces a relative clause referring to some antecedent