* 滑らか (なめらか, nama-raka): This is the most common and generally applicable word for "smooth" referring to a surface texture. Think smooth skin, a smooth surface, etc.
* 円滑 (えんかつ, enkaku): This word means "smooth" or "without problems" in the context of processes, relationships, or operations. For example, a "smooth negotiation" would be 円滑な交渉 (enkaku na kōshō).
* スムーズ (su-mu-zu): This is a loanword from English and is often used in more modern contexts, particularly when talking about processes or operations. It carries a similar meaning to 円滑 (enkaku).
To choose the right word, consider what you're describing:
* Smooth surface: 滑らか (nama-raka)
* Smooth operation/process: 円滑 (enkaku) or スムーズ (su-mu-zu)
* Smooth voice: 滑らか (nama-raka) or (depending on the nuance) なめらかで落ち着いた声 (nama-raka de ochitsuita koe - smooth and calm voice)
* Smooth transition: 円滑な移行 (enkaku na ikō) or スムーズな移行 (su-mu-zu na ikō)
Therefore, you need to provide the context to get the most accurate translation.