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.
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