Timer on metro translated into French, dear (11)
I believe the answer is:
chronometer
'timer' is the definition.
(I know that chronometer is a type of timer)
'on metro translated into french dear' is the wordplay.
'translated' is an anagram indicator.
'into' means one lot of letters goes inside another.
'french dear' becomes 'cher' ('cher' is a French term of endearment).
'on'+'metro'='onmetro'
'onmetro' anagrammed gives 'ronomet'.
'ronomet' inserted inside 'cher' is 'CHRONOMETER'.
(Other definitions for chronometer that I've seen before include "Accurate timepiece" , "Instrument measuring time" .)