Dry hay tedder spreads across field at last (10)
I believe the answer is:
dehydrated
'dry' is the definition.
(similar in meaning)
'hay tedder spreads across field at last' is the wordplay.
'spreads' indicates anagramming the letters (I've seen 'spreading' mean this).
'across' is an insertion indicator.
'at last' suggests the final letters.
The final letter of 'field' is 'd'.
'hay'+'tedder'='haytedder'
'haytedder' anagrammed gives 'dehyrated'.
'dehyrated' enclosing 'd' is 'DEHYDRATED'.
(Other definitions for dehydrated that I've seen before include "Desiccated" , "Deprived of water" , "There, daddy! (anag)" , "Dried out" , "like the Ancient Mariner?" .)