New and old American series (5)
I believe the answer is:
nexus
'series' is the definition.
(nexus is a kind of series)
'new and old american' is the wordplay.
'new' becomes 'n'.
'and' says to put letters next to each other.
'old' becomes 'ex'.
'american' becomes 'us'.
'n'+'ex'+'us'='NEXUS'
(Other definitions for nexus that I've seen before include "Connecting band" , "Focal point; link" , "Link - unsex (anag)" , "Bond, connected group" , "Unsex (anag.); a bond" .)