freemasonry

O. Henryの短編 "Transients in Arcadia" の一節です。
Perhaps there was a mystic freemasonry between the discriminating guests of the Lotus.
"freemason" に石工組合（員）とか秘密結社（員）のような意味があることは聞いた事はありますが、上の文の "freemason" の意味はそれらとはちょっと意味が離れているようです。　辞書を見ます。
・OneLook Quick Definitions: a natural or instinctive fellowship between people of similar interests ("He enjoyed the freemasonry of the Press")
・Dictionary.com: secret or tacit brotherhood; fellowship; fundamental bond or rapport: the freemasonry of those who hunger for knowledge.
・Cambridge Advanced Learner's English Dictionary: literary friendly understanding between people who are similar or do similar things; The two rivals were nevertheless united by the freemasonry of the acting profession.
石工組合や秘密結社の仲間内の親密な関係が一般的な仲間内の関係にも適用されるようになったようですね。