The only national theatre near Portsmouth (6)
I believe the answer is:
solent
'portsmouth' is the definition.
Both the definition and answer are singular nouns.
Maybe there's a link between them I don't understand?
'the only national theatre near' is the wordplay.
'the only' becomes 'sole' (I've seen this in another clue).
'national theatre' becomes 'NT' (abbreviation).
'near' means one lot of letters go next to another.
'sole'+'nt'='SOLENT'
Can you help me to learn more?
(Other definitions for solent that I've seen before include "sound" , "Water to north of IOW" , "Channel north of IOW" , "Lets on to be an English waterway" , "Waterway between Hampshire and Isle of Wight" .)