Able to be controlled, restrained, or reduced by means of a curb or limitation.
From 'curb' (from Old French 'courbe', meaning curved or bent) plus the suffix '-able' (capable of being). The original 'curb' was a chain or strap bent around a horse's jaw.
The word 'curb' comes from the curve of a horse's bridle—that's why we 'curb' enthusiasm (bend it back) and why a sidewalk curb is literally a curved edge that stops things.
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