One mistakenly printed in bold (8)
I believe the answer is:
intrepid
'bold' is the definition.
('intrepid' can be similar in meaning to 'bold')
'one mistakenly printed in' is the wordplay.
'one' becomes 'i' (Roman numeral).
'mistakenly' indicates an anagram.
'in' indicates putting letters inside.
'printed' anagrammed gives 'intrepd'.
'i' going inside 'intrepd' is 'INTREPID'.
(Other definitions for intrepid that I've seen before include "Brave and fearless" , "Novel" , "Fearless, adventurous" , "I printed this way, being daring" , "Undaunted" .)