What does the cryptic crossword clue "Mountain covered by pianist from the East (5)" mean?

The definition is "East". The wordplay uses a reversal. IANIS (reversal="IANIS") = SINAI; definition: "Mountain" The answer is SINAI.

Mountain covered by pianist from the East (5)

Guardian Cryptic #29405 | 6 Down | 2024-06-10 flower