Detective type I’ve associated with era mistakenly (7,3)
I believe the answer is:
private eye
'detective' is the definition.
(I've seen this before)
'type i've associated with era mistakenly' is the wordplay.
'associated with' says to put letters next to each other.
'mistakenly' indicates an anagram.
'type' after 'ive' is 'ivetype'.
'ivetype'+'era'='ivetypeera'
'ivetypeera' anagrammed gives 'PRIVATE EYE'.
(Other definitions for private eye that I've seen before include "50 today" , "Investigative satirical magazine" , "Freelance detective" , "Spade, say" , "Periodical" .)