Neither move, both of which comes with a failed physical designation, was a surprise.
The moves clear more than $5 million in cap space for the Seahawks, who are still hoping to re-sign Jadeveon Clowney or add one of the other available pass-rushers.
Thompson, 25, was a fourth-round pick by Seattle in 2017 and was up and down in 16 starts over the past two seasons after taking over for Earl Thomas at free safety. He made interceptions in critical moments in consecutive October victories but also had lapses in coverage that resulted in long completions, including a 50-yarder in the Seahawks' loss to Baltimore that coach Pete Carroll lamented as a "big mistake." His 2019 season ended after six games because of a shoulder injury that required labrum surgery.
Thompson no longer projected as a starter with Quandre Diggs taking over at free safety. He was scheduled to make a non-guaranteed $2.133 million in base salary this season because he met the playing-time threshold for a raise via the NFL's proven performance escalator. The Seahawks save that amount while incurring $168,000 in dead money.
Dickson was due a $3 million base salary and could have made up to $400,000 in per-game roster bonuses. Seattle incurs $867,000 in dead money with his release.
Dickson, 32, missed all of last season because of a knee injury that required surgery in August. The Seahawks briefly activated him off injured reserve in November but then put him back on IR before he played in a game.
He joined the Seahawks in 2018 as a free agent, signing a three-year deal worth $10.7 million. Dickson missed the first six games of that season, then caught 12 passes for 143 yards and three touchdowns over the final 10. The 10-year veteran previously played for Baltimore and Carolina.