Just say the word and it evokes in many the sense of an ancient grain, of ancient peoples of Mesoamerica and now a New Age Nutrition source, highly marketed.
Well, yeah sort of.
Nutritious? Yes indeed
New world? True yes and more…
Although not truly a ‘grain’ it is considered a pseudocereal , as it is not a genus considered a monocot, or more precisely a grass, like wheat, corn, barley etc
The origin of Amaranth, (Amaranthus botanically), in almost all literature is referred to as having risen in ancient Mesoamerica.
There is indeed abundant historical evidence of the huge role it has played in the ancient Aztec culture, where it was called huauhtli, not only as a major food source but also in religious ceremony as well.
The common name however is derived from Greek;
”Amaranth” derives from Greek ἀμάραντος (amárantos), “unfading”, with the Greek word for “flower”, ἄνθος (ánthos) –wiki
It also appears in the ancient writings of Aesop.
Perhaps you’ve heard of it by one species dramatic common name as “Love Lies Bleeding” (“over the garden gate”)!
Additionally it is found in records growing about the globe and in use (historically and currently) in Indonesia, Vietnam, Malaysia, Africa, India and North America.
Not only the seed but also the leaves and roots from select species are used as food as well as oil derived from the seed and dye from the flowers (Hopi red dye).
In North America ‘Pig Weed’, an Amaranth species, can be a major crop pest.
I first started growing Amaranth as an ornamental years ago when I was a field grower of cut flowers on a hundred acres in the Watsonville area. 
I grew annually about 4-5 acres of about 6 species, varieties, of the estimated 70 or so species in cultivation.
The seed is very small and I found it somewhat “fiddly” to handle.
We saved our seed each year from select plants and I was amazed, humbled and educated by our Hispanic work force (many of Mesoamerican Indian heritage) who could naturally, quickly process and clean the flower heads from a single plants flowers and extract as much as a Kilogram of seed!
A skill I knew had been learned from earlier experiences not of our farm.
I still grow Amaranth every year, mostly just for the beauty and good feeling it brings me. 
A feeling of being connected in the present with a plant whose ancestry is ancient, abundant, rich and still filled with mystery!
(BTW March is a good time to start your first crop of Amaranth locally!)

Photo © SE Popp ~ Several Amaranth species grown at home.