|eksə|fishēˌō, -i(ˌ)shō adverb (or adjective)
also ex offici·is -ishēˌēs
Etymology: Late Latin
: by virtue or because of an office or offices
all heads of departments … are called upon to serve ex officiis as members of … boards — F.A.Ogg & P.O.Ray
acting as ex officio chairman of the board