LR reached up for thing (4)
I believe the answer is:
item
'for thing' is the definition.
(an item is a thing)
'lr reached up' is the wordplay.
'lr' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'reached' becomes 'met' (I've seen this in another clue).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'met' back-to-front is 'tem'.
'i'+'tem'='ITEM'
Can you help me to learn more?
(Other definitions for item that I've seen before include "partners" , "Separate object or unit" , "two with a link" , "Single article on a list" , "Something on list" .)