The story
From a phonetic spelling of the letter S, with citalopram, since this drug is the (S)-stereoisomer of the earlier drug citalopram.
Etymology from Wiktionary, CC BY-SA 4.0.
escitalopram
Today it means: A drug that functions as an SSRI and is administered orally in the form of its oxalate C₂₀H₂₁FN₂O·C₂H₂O₄ to treat depression and anxiety. Full definition →