Strangely, three YAKU kanji have EKI as alternate on-yomi. How this situation came about, I can’t even imagine. In the following list, EKI appears first when it’s the predominant on-yomi:
益 (benefit, profit) EKI YAKU
The kun-yomi is -ma(su). The way to write masumasu, “increasingly,” in kanji is 益々!
疫 (epidemic) EKI YAKU
役 (service) YAKU EKI
A host of homophonous EKI compounds involve these kanji and other EKI characters. For instance, we have these:
     ken’eki:   検疫 (quarantine)     権益 ((one’s) interests)
     taieki:     退役 (to retire from military service)     体液 (body fluids)
     shieki:     使役 (employment)     私益 (private interest (financial))
     kōeki:     公益 (public benefit)     交易 (trade, commerce)
     ekigaku:  疫学 (epidemiology)     易学 (study of divination)
By now you’re wondering about 易, which appears in the last two rows. It can mean “to exchange” or “fortune-telling, divination,” but you likely know 易 best as yasa(shii) or yasu(i), “easy.” And now we’ve stumbled onto other homonym issues:
     yasa(shii)   易 (easy)     優 (kind)
     yasu(i)       易 (easy)     安 (cheap, calm)     廉 (cheap)
It never ends! As Mayumi in Italy likes to say, “Mamma Mia!”
                            
                            
                                
                                
                                