ability, skillfulness. The state or quality of being proficient; competence.
English proficiency is the the ability to speak, read and/or write in English. To be considered truly proficient, one should have advanced abilities in all three areas of communication.
Some measurement of your proficiency in something. Like how well your English is.
Deficiency, efficiency, residency, regency.
the word demonstrates is a verbif yoy mean demonstratives, that is the kind of pronoun