The Collaborative International Dictionary
                    Understander
                    
                        
                
                                                                    Understander \Un`der*stand"er\ ([u^]n`d[~e]r*st[a^]nd"[~e]r), n.
   One who understands, or knows by experience. [R.] 
--Dryden.
Wiktionary
                    understander
                    
                        
                
                                                                    n. One who understands something.
Usage examples of "understander".
She was partly lured by an unlooked-for understander of her plight, but equally was stung by his understanding.
Such men do not remain mere critics and understanders with their intellect.