Submissive, yours truly, by second half of journey (4)
I believe the answer is:
meek
'submissive' is the definition.
(I've seen this before)
'yours truly by second half of journey' is the wordplay.
'yours truly' becomes 'me' (the person who set this crossword).
'by' is a charade indicator (letters next to each other).
'second' becomes 're' (prefix meaning second in eg review, re-education).
'half' means to take half the letters.
'of journey' becomes 'k' (I can't justify this - if you can you should give a lot more credence to this answer).
're' halved is 'e'.
'me'+'e'+'k'='MEEK'
Can you help me to learn more?
(Other definitions for meek that I've seen before include "Patient and submissive" , "Requiring more spirit, maybe" , "Mild and timid" , "Forbearing" , "Gentle, timid" .)