Trade union support for one being instructed (5)
I believe the answer is:
tutee
'one being instructed' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'trade union support' is the wordplay.
'trade union' becomes 'TU' (abbreviation for trade union).
'support' becomes 'tee' (tee is a kind of support).
'tu'+'tee'='TUTEE'
'for' acts as a link.
Can you help me to learn more?
(Other definitions for tutee that I've seen before include "One learns from a personal teacher" , "Student, pupil" .)