Google uses it’s own definitions of synonyms gleaned from billions of natural searches and it knows what are real related search terms that people use.
Keyword stemming (adding plurals, suffixes and prefixes to keywords) and semantic keywords overlap in the sense that keyword stemming creates a context for the synonyms.
. Internally, be sure to link the synonym keywords back to your primary keyword page (or hub page). This reinforces the contextual value of the synonym.
outbound links to authority sites indicates to Google that your site is an authority site on the keyword.
Not if you: Provide relevant, personalized content; Make it interactive; Put it into the context of daily work; Use gamification techniques; Eliminate barriers such as multiple sign-ons, slow response times, etc.