Rail cut in order to reduce the length (7)
I believe the answer is:
curtail
'reduce the length' is the definition.
'curtail' can be an answer for 'reduce' (I've seen this before). I am not certain of the 'the length' bit.
'rail cut in order' is the wordplay.
'in order' indicates an anagram (the letters in a new order).
'rail'+'cut'='railcut'
'railcut' with letters rearranged gives 'CURTAIL'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for curtail that I've seen before include "Abbreviate" , "make shorter" , "'Cut short, restrict (7)'" , "Cut short like canine appendage" , "Reduce in length" .)