DuckCorp Dico

Found one definition

1.                 From Japanese-English FreeDict Dictionary ver. 0.1:
                   
   
   
                   
                     
    [news1]  [nf21]  通 /(en)tʃˈaɪniːz(ja)lˈe̞tə/,  [news1]  [nf21] つう /tsˈɯᵝɯᵝ/
   1. (adjectival nouns or quasi-adjectives (keiyodoshi))
    (noun, used as a suffix)
   connoisseur, authority
   2. (counter)
   counter for letters, notes, documents, etc.