"properest" in the adjective sense
1. proper
marked by suitability or rightness or appropriateness
"proper medical treatment"
"proper manners"
2. proper
having all the qualities typical of the thing specified
"wanted a proper dinner, not just a snack"
"he finally has a proper job"
3. proper
limited to the thing specified
"the city proper"
"his claim is connected with the deed proper"
4. proper, right
appropriate for a condition or purpose or occasion or a person's character, needs
"everything in its proper place"
"the right man for the job"
"she is not suitable for the position"
Source: WordNet® (An amazing lexical database of English)
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