The measurer met with ultimate disaster (5)
I believe the answer is:
meter
'the measurer' is the definition.
(I've seen this in another clue)
'met with ultimate disaster' is the wordplay.
'met with' becomes 'mete' (I am not sure about this - if you are sure you should believe this answer much more).
'ultimate' says to take the final letters.
The final letter of 'disaster' is 'r'.
'mete'+'r'='METER'
Can you help me to learn more?
(Other definitions for meter that I've seen before include "Device to measure quantity used of fluid, electricity etc" , "Apparatus for measuring" , "Measuring device as for electricity consumption" , "Device for recording, say, usage (5)" , "Measuring device, say for electricity usage" .)