challenge

As a verb challenge

is .

As a noun obstruction is

the act of obstructing, or state of being obstructed.

As a noun puzzle

is puzzle.

As a verb challenge is

.

As verbs the difference between challenge and appeal

is that challenge is while appeal is (obsolete) to accuse (someone of something).

As a noun appeal is

(legal) (a) an application for the removal of a cause or suit from an inferior to a superior judge or court for re-examination or review (b) the mode of proceeding by which such removal is effected (c) the right of appeal (d) an accusation; a process which formerly might be instituted by one private person against another for some heinous crime demanding punishment for the particular injury suffered, rather than for the offense against the public (e) an accusation of a felon at common law by one of his accomplices, which accomplice was then called an approver.

As a verb challenge

is .

As a noun cassation is

the abrogation of a law by a higher authority; annulment or cassation can be (music) piece of instrumental music of the eighteenth century similar to the serenade, and often performed out of doors.

As verbs the difference between challenge and subvert

is that challenge is while subvert is to overturn from the foundation; to overthrow; to ruin utterly.

As a noun subvert is

an advertisement created by subvertising.

As verbs the difference between challenge and criticise

is that challenge is while criticise is to evaluate (something), and judge its merits and faults.

As a verb challenge

is .

As a noun peril is

peril, danger.

As verbs the difference between challenge and elude

is that challenge is while elude is .

As a verb challenge

is .

As a noun protest is

protest.

As a noun revolution

is revolution.

As a verb challenge is

.