Hoover

- hoo·ver [hoo-ver]
–verb: to clean with a vacuum cleaner (Chiefly British)
It is in fact a trademark brand name of a vacuum cleaner. This brand was named after the American industrialist, William H. Hoover (1849-1942) who commercialized vacuum cleaners as one of the "must-have" household items.
Xerox

- xe·rox [zeer-oks]
-noun or verb: a name for a copying machine or the act of reproducing printed, written, or pictorial matter by xerography.
This is a trademark brand name for a copy machine. "Xerox" is an invented name from the word xerography which came from the Greek radicals xeros (dry) and graphos (writing), as there are no liquid chemicals involved in the copying process.
Thermos

- ther·mos [thur-muhs]
–noun: a vacuum bottle or similar container lined with an insulating material, such as polystyrene, to keep liquid hot or cold
This is a trademark brand name of a vacuum flask. The word is actually derived from the Greek word thermo or "hot".
Prozac

- pro·zac [proh-zak] -noun: a brand of fluoxetine hydrochloride
This is a trademark brand name for a type of drug prescribed for depression. However, it is often widely used to refer to other drugs that treat similar cases of depression.
Spandex

- span·dex [span-deks]
–noun: a synthetic fiber composed of a long-chain polymer, used chiefly in the manufacture of garments to add elasticity
This is a trademark of a type of polyurethane fabric. However, it is also widely used to refer to other stretchy fabric material.
Jello

- jell-O [jel-oh]
-noun: brand of dessert made from a mixture of gelatin, sugar, and fruit flavoring, dissolved in hot water and chilled until firm
This is an American trademark brand name, i.e. Jell-O. It is also used to refer to other similar types of jelly desserts.
Tampax

- tampax [tam-pax]
-noun: tampon used to absorb menstrual flow
This is a trademark brand name for a tampon but it is also widely used as a generic name to refer to similar types of sanitary tampons.
Band-Aid

- band-Aid [band-eyd]
-noun: adhesive bandage with a gauze pad in the center, used to cover minor abrasions and cuts
This is a trademark brand name, widely used to refer to other similar types of bandages.
Viagra

- vi·ag·ra [vahy-ag-ruh]
-noun: sildenafil citrate, used to treat impotence
This is a trademark brand name, widely used to refer to other similar types of male potency drugs. It is also said that the name comes from the word virility and Niagara.