billow — bellow — below
“Billow” (for the right pronunciation, please click here)

some billows (huge waves)
as a noun means ‘huge wave; a great rolling mass of smoke’; and as a verb, it means ‘to swell out – to become large on all sides at a time’,
e.g.
Billows of black smoke rose from the burning buildings.
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“Bellow” (for the right pronunciation, please click here)

a pair of bellows
as a noun is (usually used in the plural – bellows) ‘an apparatus to blow air into a fire to make the fire burn quickly or with more heat’; and as a verb it means ‘to make a deep, loud sound, usually made by bulls’,
e.g.
A blacksmith uses a pair of bellows.
Can you hear the bulls bellowing in the fields?
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“Below” (for the right pronunciation, please click here)

below
can be used as an adverb, preposition or an adjective to mean ‘in a lower level, position; under the surface of something; lower than a standard quality or efficiency’,
e.g.
The water level is below danger mark.
He is a below average student; he must work harder.
