Place restrictions on (5)
(Other definitions for limit that I've seen before include "Place bound on" , "Restrict - term" , "Constrain" , "Breaking point" , "Ceiling" .)
'place restrictions on' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for curbs that I've seen before include "Restrains" , "Place restrictions on" , "Keeps in check" .)
(Other definitions for curtail that I've seen before include "Reduce in extent" , "Shorten, abridge" , "Cut short like canine appendage" , "Impose a restriction on" , "'Cut short, restrict (7)'" .)