Giant insect covering a couple of metres (7)
I believe the answer is:
mammoth
'giant' is the definition.
(thesaurus)
'insect covering a couple of metres' is the wordplay.
'insect' becomes 'moth' (moth is a kind of insect).
'covering' indicates putting letters inside.
'couple of' says to double the letters.
'metres' becomes 'm'.
'm' duplicated is 'mm'.
'a'+'mm'='amm'
'moth' enclosing 'amm' is 'MAMMOTH'.
(Other definitions for mammoth that I've seen before include "Brobdingnagian" , "Extinct type of elephant" , "Large extinct elephant" , "Prehistoric woolly elephant" , "Gigantic - extinct animal" .)