This is the 1516th most frequent Chinese word.
臣
"臣" means "minister" or "subject" (in a monarchic context).
In this sentence, '臣' is used as an honorific referring to oneself, indicating humility and respect.
臣以为此计可行。
I believe this plan is feasible.
Here, '臣' refers to officials serving under a monarch, reflecting its traditional usage.
古时,臣对君主忠诚是一种美德。
In ancient times, loyalty of officials to the emperor was considered a virtue.
In this case, '臣' portrays the speaker humbly referring to themselves in a hierarchical context.