The 24-year-old left wing heads back to Western New York, where he played college hockey with Canisius.
The five-foot-eight Conacher has suffered the dreaded sophomore slump this season, with just four goals and 16 assists in 59 games. He impressed as an undrafted rookie in 2013, with 11 goals and 18 assists in 47 games with Tampa Bay and Ottawa, adding three goals in eight playoff games for the Senators.
Ottawa acquired Conacher and a draft pick 11 months ago in a trade with the Lightning for goalie Ben Bishop.
Bishop has gone on to star for the Tampa Bay Lightning this season, but at the time of last year's trade he was No. 3 on Ottawa's depth chart behind Craig Anderson and Robin Lehner.
The pick was used to draft Swedish forward Tobias Lindberg last year.
In the other NHL waiver claim made Wednesday, Boston picked up defenceman Corey Potter.
Potter was waived by Edmonton the previous day, having tallied five assists in 16 games in the NHL this season.
The 30-year-old has also played for the New York Rangers. For his career, he's scored eight goals and 24 assists in 120 regular-season games, with 53 penalty minutes.