True about first half of semi being close again (6)
I believe the answer is:
reseal
'being close again' is the definition.
(to seal or close again)
'true about first half of semi' is the wordplay.
'true' becomes 'real' (similar in meaning).
'about' indicates putting letters inside.
'first half of' suggests halving the letters.
'semi' halved is 'se'.
'real' enclosing 'se' is 'RESEAL'.
(Other definitions for reseal that I've seen before include "Close again tightly" , "Close securely again" .)