IPA: /hɜːˈmɛtɪkəl/
KK: /hɜrˈmɛtɪkəl/
Relating to something that is airtight or sealed off from outside influences, often used in a metaphorical sense to describe something that is obscure or difficult to understand.
The scientist used a hermetical seal to ensure that no air could enter the container.
Hermetical → It is derived from "Hermes" (the Greek god associated with knowledge and communication) and the suffix "-ical" (meaning pertaining to). The term originally refers to things related to Hermes, particularly in the context of alchemy and secret knowledge, hence the meaning of being sealed or concealed.
Think of Hermes, the god of knowledge, and remember that 'hermetical' means pertaining to secret or concealed knowledge.