Tight-mouthed and Tight-lipped

Tight-mouthed adjective - Given to keeping one's activities hidden from public observation or knowledge.

Tight-lipped and tight-mouthed are semantically related. In some cases you can use "Tight-lipped" instead an adjective phrase "Tight-mouthed".

Tight-lipped adjective - Tending not to speak frequently (as by habit or inclination).

Tight-mouthed and tight-lipped are semantically related. You can use "Tight-mouthed" instead an adjective phrase "Tight-lipped".