(Lexemes)

• fast—adj. 'swift; quick; speedy'
• swift—adj. 'rapid; fast'

Here is how the circularity can be resolved by the addition of an analytic definition and supplemental information:

• fast—adj. 'rapid in movement or action, often referring to the person or thing that moves; swift; quick; speedy'
• swift—adj. 'moving or capable of moving with great speed, often in a smooth and easy manner; rapid; fast'