Historian understood by you and me (7)
I believe the answer is:
tacitus
'historian' is the definition.
(Roman historian)
'understood by you and me' is the wordplay.
'understood' becomes 'tacit' (I've seen this before).
'by' means one lot of letters go next to another.
'you and me' becomes 'us'.
'tacit'+'us'='TACITUS'
(Other definitions for tacitus that I've seen before include "Roman politician and historian" , "Roman historian, annalist" , "Writer" , "Old historian" , "Old history master" .)