Modern tools today are made to make work less insufferable.
The opponent is insufferable because he is well trained.
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1) It is insufferably boring.
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That insufferably haughty provocateur was the proudest man I'd
ever met.
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No. Suffers is a verb form. Adverb forms would include
insufferably and sufferingly.
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A greenhouse is warmer and usually more humid than being
outside. The glass walls let solar heat in but tend not to let it
out. Except in the summer, greenhouses do not become insufferably
hot.