A triangular piece of material inserted into a garment or fabric for added strength or expansion at stress points.
From Old French 'gousset' (armor joint), derived from Latin 'gutta' (drop), likely because the small triangular pieces resembled water drops; eventually became 'gusset' in English.
The 'gusset' exists in your underwear, your tent corners, and medieval armor—it's one of humanity's oldest sewing innovations because concentrating stress at one point usually means tears at that exact spot.
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