First in unit to fail training (7)
I believe the answer is:
tuition
'training' is the definition.
(I've seen this before)
'first in unit to fail' is the wordplay.
'first in' becomes 'i' (1st letter of 'in').
'fail' indicates an anagram (I've seen 'failing' mean this).
'i'+'unit'+'to'='iunitto'
'iunitto' anagrammed gives 'TUITION'.
(Other definitions for tuition that I've seen before include "(Individual) instruction" , "Lessons" , "practice" , "Training" , "Teaching, often one-to-one" .)