19. either
    As an adjective, it can mean "one or the other of two," as in "you either passed or failed your test"
    It can also mean "each of two; the one and the other" as in "trees on either side of the river."
20. eventual
    Current use, applied to a future event or occurrence, means "inevitable, given enough time"
    An older usage, applied in the same situation, means "possible, subject to contingencies"
21. execute
    To execute a person is to end their life
    To execute a program is to start it
22. fast
    Fast can mean either "to move or do quickly" or it can mean "to not move," as in "holding fast"
    As an adjective, it can also convey both meanings: "The rabbit is fast;" "The door is fast."

23. first degree
    Most severe (e.g., murder)
    Least severe (e.g., burn)
24. fix
    Fix can mean either "to mend"
    Or it can mean "to break," as in "I'll fix you"
25. flank
    Flank can either mean to protect the sides of something
    Or to attack the flanks
26. for
    For can mean either "to cause" or "to alleviate
    A tranquilizer is used for relaxation; aspirin is used for pain
27. flog
    It can mean to criticize harshly
    It can mean to promote aggressively