God cross having to secure a chest (6)
I believe the answer is:
thorax
'chest' is the definition.
(I know that thorax can be written as thorax)
'god cross having to secure a' is the wordplay.
'god' becomes 'thor' (Thor is an example).
'cross' becomes 'x' (X is cross-shaped).
'having to secure' is an insertion indicator (inserted letters are secured).
'thor'+'x'='thorx'
'thorx' placed around 'a' is 'THORAX'.
(Other definitions for thorax that I've seen before include "Between the neck and belly" , "Middle section of insect's body" , "Insect's upper body" , "Part of the body between the head and abdomen" , "Upper part of the trunk" .)