The story
From (iso)pen(tyl) + -ciclovir (“bicyclic heterocycle compound”).
Etymology from Wiktionary, CC BY-SA 4.0.
penciclovir
Today it means: A guanine analogue antiviral drug C₁₀H₁₅N₅O₃ that is used mostly topically for the treatment of recurrent herpes labialis. Full definition →