Horrid chant about writer's insides (9)

'horrid' is the definition.
Both the definition and answer are adjectives. Perhaps you can see a link between them that I don't see?

'chant about writer's insides' is the wordplay.
'chant' becomes 'sicking' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'about' means one lot of letters goes inside another.
'writer's' becomes 'pen's' (something which writes).
'insides' means to look at the middle letters (I've seen 'inside' mean this).
The central letters of 'pens' are 'en'.
'sicking' placed around 'en' is 'SICKENING'.

Can you help me to learn more?