Crossword Genius

Measure many a wild tree (5)

Ross

I believe the answer is:

meter

'measure' is the definition.
(I know that measure can be written as meter)

'many a wild tree' is the wordplay.
'many' becomes 'm' (Roman numeral for a thousand).
'a wild' is an anagram indicator.
'tree' with letters rearranged gives 'eter'.
'm'+'eter'='METER'

(Other definitions for meter that I've seen before include "Device for recording, say, usage (5)" , "Device that measures, say, electricity usage" , "Apparatus for measuring" , "Gauge" , "Measuring device as for electricity usage (5)" .)

I've seen this clue in the Evening Standard.
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