The word "hidden" is the past tense of an irregular verb. Irregular verbs do not follow the typical pattern of adding "ed" to form the past tense, as regular verbs do. Instead, irregular verbs have their own unique forms for the past tense. To determine the past tense of an irregular verb, you would typically consult a list of irregular verbs or refer to a dictionary. In this case, "hidden" is the past tense form of the verb "hide."
