search ranking strategy

[CarmenCorre]

Is your feature request related to a problem? Please describe.
When we want to search a term wich is not a Preferred name, it is too far down in the results. Example: "oak" in thesaurus INRAE is a synonyme, its preferred name is "quercus" -> for thesaurus INRAE it comes after "Oak tree".

Describe the solution you'd like
In determining the results ranking, synonymes and Prefered name should be considered alike. In other words, matching the prefered term or the synonym should lead to the same place in the results ranking