
incumbent
ɪnˈkʌmb(ə)nt/
adjective
adjective: incumbent
-
1.necessary for (someone) as a duty or responsibility.“the government realized that it was incumbent on them to act”
synonyms: 
binding, obligatory, mandatory, necessary, compulsory, required,requisite, essential, imperative “it is incumbent on the government to give a clear lead”
antonyms: optional -
3.(of a company) having a sizeable share of a market.“powerful incumbent airlines”
Origin
late Middle English (as a noun): from Anglo-Latin incumbens, incumbent-, from Latinincumbere ‘lie or lean on’, from in- ‘upon’ +
