Pronunciation: [ uh-fish-yuh-nah-doh ]
Definition: noun
a person who is very knowledgeable and enthusiastic about an activity, subject, or pastime

Origin: Mid 19th century; Latin
Etymology: from Spanish, ‘amateur’, past participle of aficioner ‘become fond of’ used as a noun, based on Latin affectio(n-) ‘(favorable) disposition towards’
Usage:

Synonyms:
devotee
adorer
enthusiast
fan
connoisseur
expert
authority
specialist
pundit
Antonyms:
hater
unenthusiastic
uninformed
Example: Sally was an aficionado of the finest wines in the world.