Secure
Secure adjective - Not exposed to the threat of loss or injury.
Usage example: the fortress was thought to be secure against attack
Sound is a synonym for secure in certain topic. In some cases you can use "Sound" instead an adjective "Secure", when it comes to topics like fastened, continue, strong.
Cite this Source
Sound and Secure. (2016). Retrieved 2026, July 21, from https://thesaurus.plus/related/secure/sound
Secure & Sound. N.p., 2016. Web. 21 Jul. 2026. <https://thesaurus.plus/related/secure/sound>.
Sound or Secure. 2016. Accessed July 21, 2026. https://thesaurus.plus/related/secure/sound.
Google Ngram Viewer shows how "secure" and "sound" have occurred on timeline