The league announced the fine, the maximum allowed per rules of the collective bargaining agreement, on Friday morning.
Lucic appeared to make the vulgar gesture toward fans at the Bell Centre as he skated to the penalty box after being whistled for boarding Alexei Emelin in the third period of the Bruins' 6-4 loss.
The incident escalated the existing enmity between the teams and their respective fan bases. The clubs met in the Eastern Conference semifinals last spring and heated words were exchanged in the handshake line after the Habs bounced the Bruins from the playoffs.
Lucic did not speak to reporters after Thursday night's game.
Rask Pulled In Bruins' Loss
The Bruins' Tuukka Rask was pulled after giving up five goals, including two each to the Canadiens' Brendan Gallagher and P.A. Parentea, in Montreal's 6-3 win over Boston.