Tip off old prince - essentially FBI's given up (5)
I believe the answer is:
alert
'tip off' is the definition.
(I've seen this in another clue)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for alert that I've seen before include "Watchful and bright" , "Quick to notice" , "'Attentive, vigilant (5)'" , "alarm" , "'Attentive, watchful (5)'" .)