Keep watch on idiot in Othello, for one (7)
I believe the answer is:
monitor
'keep watch on' is the definition.
(to monitor is to keep an eye on)
'idiot in othello for one' is the wordplay.
'idiot' becomes 'nit' (I've seen this before).
'in' means one lot of letters goes inside another.
'othello for one' becomes 'moor' (Shakespeare's Othello is a Moor).
'nit' going inside 'moor' is 'MONITOR'.
(Other definitions for monitor that I've seen before include "Observe over time" , "Keep a check on" , "in-class help" , "Keep track of" , "record" .)