Returning to action after a nearly two-week hiatus, the Tribe (6-4) took control of the game late in the first half with a 17-4 run. William & Mary opened the second half with an 11-2 spurt fueled by Thornton, who hit a 3-pointer, a layup and went 4 for 4 from the foul line in just under three minutes.
Julian Boatner contributed 15 points for the Tribe, which has won five of its last six games.
Goucher, a Division III team, kept the score close through much of the first half but couldn't control the boards, getting outrebounded 46-27 and ending the night just 23 of 60 from the field.
Maryland point guard Melo Trimble, considered a lock to leave the program before struggling in the second half last season, has withdrawn from the NBA draft and will return for his junior season.
Louisville's Chinanu Onuaku, who recently underwent a medical procedure to correct a heart rhythm issue detected during the combine, will keep his name in the NBA draft pool.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.