To identify the word that most closely resembles "esoteric," we will examine the provided choices:
- Obvious: Characterized by being readily apparent or easily comprehensible; this is the antonym of esoteric.
- Mysterious: Defined by being hard to comprehend or articulate, often linked to subjects unknown to the general populace, thereby paralleling the definition of esoteric.
- Commonplace: Signifying ordinariness or lack of distinction, which contrasts with the exclusive character of esoteric.
- Confidential: Pertaining to information known only to a select few or kept secret; while related, it is not as precise a synonym as mysterious.
The most appropriate selection is Mysterious, as "esoteric" denotes concepts or knowledge understood by or intended for a select, limited audience, which aligns with the connotations of obscurity and mystery.