Element, large one, hit out with hesitation (7)
I believe the answer is:
lithium
'element' is the definition.
(I know that lithium is a type of metal)
'large one hit out with hesitation' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'one' becomes 'I' (Roman numeral).
'hit out' becomes 'thi' (anagram of 'hit').
'with' is a charade indicator (letters next to each other).
'hesitation' becomes 'um' (um is said in hesitation).
'l'+'i'+'thi'+'um'='LITHIUM'
(Other definitions for lithium that I've seen before include "Silver-white metal (symbol: Li)" , "Lightest metallic element" , "Lightest-known metal" , "Light metal element" , "Soft silvery element" .)