One going on to choose Civil Service’s visionary study (6)
I believe the answer is:
optics
'visionary study' is the definition.
'optics' can be an answer for 'study' (optics is a kind of study). I'm not certain of the 'visionary' bit.
'one going on to choose civil service's' is the wordplay.
'one' becomes 'i' (Roman numeral).
'going on' says to put letters next to each other.
'to choose' becomes 'opt' (both can mean to pick something).
'civil service' becomes 'CS' (abbreviation).
'i' put after 'opt' is 'opti'.
'opti'+'cs'='OPTICS'
Can you help me to learn more?
(Other definitions for optics that I've seen before include "Drink measuring devices" , "Scientific studies of light and vision, the eyes" , "Spirit measures" , "Organs of sight, eyes" , "Devices attached to bottles to measure out spirits" .)