Wiktionary
tangentiality
n. (context medicine English) A mental condition in which one tends to digress from the topic under discussion, especially by word association.
Wikipedia
Tangentiality
Tangentiality as a medical symptom is a physical symptom observed in speech that tends to occur in situations where a person is experiencing high anxiety, as a manifestation of the psychosis known as schizophrenia, in dementia or in states of delirium.