In Hebrew: 'To Conceal'

לְהַסְתִּיר The Talmud connects the name of the Purim story's heroine, אֶסְתֵּר - Esther - with the concept of concealment, the root of which is ס.ת.ר (s.t.r). Here's a Wikipedia article containing various explanations for the name of אסתר.Deriving from the ס.ת.ר root, we have the verb לְהַסְתִּיר - to conceal or to hide. להסתיר is an active-causative הִפְעִילverb. For example:

הִיא הִסְתִּירָה אֶת הַמֵּידַע מֵהַתִּקְשׁוֹרֶת. She concealed the information from the media. Something concealed is מֻסְתָּר - a passive-causative הֻפְעַל gerund. For example:

הוּא נוֹשֵׂא אֶקְדַח מֻסְתָּר. He is carrying a concealed weapon. A synonym of להסתיר is לְהַחְבִּיא - to hide (something), usually referring to hiding something physical. Visit Ktzat Ivrit.