Stony-faced describes a person whose face shows nothing at all — no smile, no anger, no sign of what they are feeling. The picture is a face made of stone: still, hard, unmoving. It is almost always used about someone in a situation where you would expect a reaction, and that is what makes it powerful. A stony-faced judge listens to a plea without moving. A stony-faced father sits through his son's apology. A stony-faced crowd watches a speech and does not clap. The word usually suggests disapproval underneath the stillness — not that the person feels nothing, but that they are refusing to show warmth. That is the difference between this and a word like 'blank' or 'expressionless', which can simply mean absent-minded. It works before a noun ('a stony-faced official') and after the verb be ('she stayed stony-faced throughout'), and you often see it added to a sentence about someone else's action: 'he told the joke; she remained stony-faced'. Keep the hyphen. The tone is neutral to slightly literary — you meet it often in novels and news reports, and it is perfectly normal in speech too.