Trend-line anomaly (4)
I believe the answer is:
blip
'trend-line anomaly' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for blip that I've seen before include "Unexpected and minor temporary deviation" , "Echo displayed on a radar screen" , "often seen on radar screen" , "Bright spot on screen" , "Glitch" .)