This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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v. To make or become stiff or stiffer.

v. To make stiff.

v. To become stiff.

v. To make stiff; to make less pliant or flexible.

v. To inspissate; to make more thick or viscous.

v. To make torpid; to benumb.

verb-intransitive. To become stiff or stiffer, in any sense of the adjective.

To become stiff.

To become less soft or fluid; grow thicker or harder; become inspissated: as, jellies stiffen as they cool.

To become steady and strong: as. a stiffening breeze.

To become unyielding; grow rigid, obstinate, or formal.

To become higher in price; become firmer or more unyielding: as, the market stiffens.

To make stiff.

To make rigid, constrained, formal, or habitual.

To make more thick or viscous; inspissate: as, to stiffen paste.

To make stubborn or obstinate.

v. become stiff or stiffer

v. make stiff or stiffer

v. restrict

"But the title might stiffen a cock or two in Dubuque."

stiffened    stiffening    stiffens   

limit    throttle    trammel    restrain    bound    restrict    confine   

harden   

stiff   

inspissate    benumb    harden    suffocate    extinguish    repress    suppress   

griffon   

tighten    twitch    weaken    soften    shiver    widen    pudgy    knobby    rock-hard    tremble