lanĉi

A young word, and honestly so. Lanĉi is not in Zamenhof and it is not in the Fundamento. It arrived with the commercial and journalistic register - the Reta Vortaro carries it, the newer dictionaries carry it, and the modern Esperanto press uses it without comment - so it is a perfectly usable word. But it is a twentieth-century import into a language that already had ways of saying this, and knowing the alternatives is what stops you reaching for a loan out of habit.

What it replaced, and where the older words still win. For a boat, the precise verb is enakvigi, to put into water. For a product, surmerkatigi is to put on the market. For anything at all, ekigi is to set going. Those builds are transparent to a speaker who has never met lanĉi, which is the argument for them; lanĉi is shorter and instantly recognisable to anybody with English or French, which is the argument against. Both arguments are real and the language has quietly kept all four words.

Grammar note. It is transitive: you launch something. The thing that gets launched takes -n, and the passive estis lanĉita is how you say it the other way round.