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Webster 1913 Edition

Noun.

One who, or that which, hems with a needle.

Specifically:

(a)

An attachment to a sewing machine, for turning under the edge of a piece of fabric, preparatory to stitching it down.

(b)

A tool for turning over the edge of sheet metal to make a hem.

hemmer ‎(plural hemmers)

One who, or that which, hems.
A device, attached to a sewing machine, that turns over the edge of a fabric before stitching it down
A tool for turning over the edge of sheet metal to make a hem.

hemmer