At sea a way to plot and exact revenge (4,9)
I believe the answer is:
dead reckoning
'exact revenge' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'at sea a way to plot' is the wordplay.
I cannot quite understand how this works, but
'at' could be 'on' (location) and 'on' is found in the answer.
'a' is within the answer.
'way' could be 'n' (Compass direction - North) and 'n' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'and' is the link.
Can you help me to learn more?
(Other definitions for dead reckoning that I've seen before include "Estimation of position at sea by reference to course steered and distance run" , "Navigation without using the stars" , "at sea, it establishes one's position" , "navigational calculation" , "Estimating sea position blind" .)