Huge people in rebuilt semi (7)
I believe the answer is:
immense
'huge' is the definition.
(synonyms)
'people in rebuilt semi' is the wordplay.
'people' becomes 'men' (men are people).
'in' is an insertion indicator.
'rebuilt' indicates anagramming the letters.
'semi' is an anagram of 'imse'.
'men' placed inside 'imse' is 'IMMENSE'.
(Other definitions for immense that I've seen before include "Huge, vast" , "Very big, really huge" , "Unusually great in size" , "Unusually large or great" , "Huge, very big indeed" .)