Both Uses

mystic
in
Looking for Alaska
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Holly hung with the Weekday Warriors, which explains why I'd previously said about two words to her in my life, but she just came in without knocking and said that she'd had a mystical indicator of Alaska's presence.†
p. 168.8

mystical = relating to realities beyond scientific understanding OR inspiring a sense of wonder or mystery; or beyond human comprehension
I scribbled Okay on my own notebook and then turned to a blank page as Dr. Hyde started talking about Sufism, the mystical sect of Islam.†
p. 173.6 *

Definitions:

(1) (mystic)
a person who seeks or claims to have direct spiritual insight beyond ordinary understanding; or describing an experience that feels deeply spiritual, mysterious, or otherworldly

In common usage, mystic is more likely to be used in reference to a practitioner of a less mainstream religion than a more mainstream religion -- possibly because the former is more mysterious to the writer.
(2) (meaning too rare to warrant focus)