Type of solid fish almost, not about to be caught (8)
I believe the answer is:
platonic
'type of solid' is the definition.
'fish almost not about to be caught' is the wordplay.
I cannot really see how this works, but
an anagram of 'not' is 'ton' which is within the answer.
'about' could be 'c' (abbreviation for 'circa') and 'c' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for platonic that I've seen before include "Relating to a particular Greek philosopher" , "according to one philosopher" , "Concerning old Greek philosopher or a soul relationship" , "Descriptive of a friendship-only relationship" , "No-sex" .)