さも is a somewhat literary and emphatic adverb that means 'really' or 'as if'. It is used to say that someone's outward behavior or expression strongly shows an inner feeling, often when that feeling may not be genuine. For example, if someone speaks 'as if' they are happy, you say さも楽しげに話す. It adds a dramatic, almost narrative tone, so you'll often find it in novels or formal writing, but it can also be used in speech to sound emphatic.

In meaning, it's similar to まるで (as if) or 本当に (really), but さも is stronger and more specific. It implies an appearance that is striking enough to be taken as real, or even exaggerated. For instance, さも知っているかのように means 'as if he really knows' — the person may not know, but his manner says otherwise. The attachment is simple: place さも right before the verb or adjective that describes the appearance or manner. It often combines with げ (seeming) or ように (as if) to form phrases like さも楽しげに, さも当然のように.

This word is not used in casual everyday conversation; it sounds literary or dramatic. If you use it in a casual chat, you'll sound like you're reading a novel. But in essays, news, or storytelling, it's fine.