Curl of hair (5)
(Other definitions for tress that I've seen before include "Switch" , "Curl - lock" , "is a bit of a shock" , "Long piece of hair" , "Bit of hair" .)
'curl of hair' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ringlet that I've seen before include "Long curl of hair" , "Cluster of hair" , "sort of lock" , "A curl - kind of tingler" , "Hair feature" .)