1. most reliable, sensible, or well-founded (superlative of sound)
2. most physically strong or healthy (superlative of sound)
3. deepest or most complete, especially referring to sleep (superlative of sound)

Examples

• She gave the soundest advice I’ve ever received.
• This is the soundest investment strategy for beginners.
• The old oak tree has the soundest trunk in the forest.
• He was in his soundest sleep when the alarm went off.
• The soundest reasoning led them to the correct conclusion.
• After the storm, only the soundest buildings remained intact.
• The baby enjoyed her soundest nap of the day.