Bottom section of genuine Thermos twists (10)

I believe the answer is:
nethermost
'bottom' is the definition.
(similar in meaning)
'section of genuine thermos twists' is the wordplay.
'section of' indicates a hidden word.
'NETHERMOST' is hidden in the letters of 'genuine thermos twists'.
(Other definitions for nethermost that I've seen before include "located in lowest position" , "at the bottom of the pile" .)