The possibly-appropriate word vial has already been suggested, but I think phial, "glass vessel or bottle, especially a small bottle for medicines", is a better choice for fantasy fiction. Also consider ampoule, flask, and cuvette, "a small vessel with at least two flat and transparent sides".
Also note a number of related words that appear in a passage in Chapter 9 of The Nursing Home Murders by Ngaio Marsh:
"...Now I understand that the jar, bottle, or pot containing the
"It was an ampoule," said Jane.
"So it was—and the pipkin, cruse, or pottle containing hyoscine were
on the table. ..."
From en.wiktionary, jar in sense 2 means "A small, approximately cylindrical container, normally made of clay or glass, for holding fruit, preserves, etc., or for ornamental purposes. ... Synonyms: cruse, pot".
From en.wiktionary, bottle means "A container, typically made of glass or plastic and having a tapered neck, used primarily for holding liquids". [Many bottles have straight rather than tapered sides. Certain metal containers are referred to as water bottles, fuel bottles, etc.]
From en.wiktionary, pipkin means "A small earthen pot".
From en.wiktionary, cruse means "A small jar used to hold liquid, such as oil or water".
Per en.wiktionary, pottle means "A small pot or other receptacle, e.g. for strawberries".