Moralist discovered in the up-train (7)
I believe the answer is:
puritan
'moralist' is the definition.
(I've seen this before)
'in the up-train' is the wordplay.
'in the' becomes 'pu' (I am not sure about this - if you are sure you should believe this answer much more).
'up' indicates anagramming the letters (letters get chucked up).
'train' is an anagram of 'ritan'.
'pu'+'ritan'='PURITAN'
'discovered' acts as a link.
Can you help me to learn more?
(Other definitions for puritan that I've seen before include "Strictly moral person" , "Adherent ot strict religous principles, opposed to sensual pleasures" , "One forgoing pleasure" , "Strict person for whom pleasure is sinful" , "Very strict person who sees fun as sinful" .)