Eight-footer in chair and out (8)
I believe the answer is:
arachnid
'eight-footer' is the definition.
I can't judge whether this defines the answer.
'chair and out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'chair'+'and'='chairand'
'chairand' anagrammed gives 'ARACHNID'.
'in' is the link.
Can you help me to learn more?
(Other definitions for arachnid that I've seen before include "Spider or scorpion, e.g." , "Class of animals including spiders and scorpions" , "Group including spiders and scorpions" , "Member of the spider family" , "Spider in a chard" .)