The act or process of attempting to modify or regulate something; an adjustment or regulation.
From attemper + -ment suffix. This follows standard English derivational patterns but is quite rare in modern usage.
This is a perfectly logical English word formation that just never caught on—we have 'temperament' (your personality) and 'temper' (to adjust), but 'attemperament' sounds so clunky that writers chose other options instead.
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