The term "sneaky link" refers to a secret or discreet romantic or sexual relationship, often one that is kept hidden from others. It can imply a sense of stealth or confidentiality in the relationship, suggesting that the individuals involved want to keep their connection away from public scrutiny or disapproval.
The term "sneaky link" combines "sneaky," which comes from the Middle Dutch word "snecken" meaning to steal, and "link," which has its origins in Old English "hlinc" meaning a connection or relationship. The modern usage reflects contemporary slang that has evolved to describe discreet relationships.