Etymology
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bloom (n.1)

"blossom of a plant," c. 1200, a northern word, from a Scandinavian source akin to Old Norse blomi "flower, blossom," also collectively "flowers and foliage on trees;" from Proto-Germanic *blomon (source also of Old Saxon blomo, Middle Dutch bloeme, Dutch bloem, Old High German bluomo, German Blume, Gothic bloma), from PIE *bhle- (source also of Old Irish blath "blossom, flower," Latin flos "flower," florere "to blossom, flourish"), extended form of root *bhel- (3) "to thrive, bloom." Related to Old English blowan "to flower" (see blow (v.2)).

Not extended like 'flower' to a whole 'flowering plant', and expressing a more delicate notion than 'blossom', which is more commonly florescence bearing promise of fruit, while 'bloom' is florescence thought of as the culminating beauty of the plant. Cherry trees are said to be in blossom, hyacinths in bloom. [OED]

Transferred sense, of persons, "pre-eminence, superiority," is from c. 1300; meaning "state of greatest loveliness" is from early 14c.; that of "blush on the cheeks" is from 1752. Old English had cognate bloma, but only in the figurative sense of "state of greatest beauty;" the main word in Old English for "flower" was blostm (see blossom (n.)).

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bloom (n.2)
"rough mass of wrought iron," from Old English bloma "lump of metal; mass," which is of unknown origin. Identical in form to bloom (n.1), and sometimes regarded as a secondary sense of it, but evidence of a connection is wanting.
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bloom (v.)
mid-13c., blomen, "bear flowers, blossom, be in flower," from an Old Norse noun from the same source as bloom (n.1). Related: Bloomed; blooming.
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bloomer (n.)
1730, "plant which blooms," agent noun from bloom (v.).
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abloom (adj.)

"in blossom, in a blooming state," 1855, from a- (1) + bloom (v.).

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blooming (adj.)
late 14c., "that is in flower, flourishing," present-participle adjective from bloom (v.). Meaning "full-blown" (often a euphemism for bloody) is attested from 1882.
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blossom (n.)
c. 1200, from Old English blostm, blostma "a flower of a plant," from Proto-Germanic *blo-s- (source also of Middle Low German blosom, Dutch bloesem, German Blust), from PIE *bhlow-, extended form of root *bhel- (3) "to thrive, bloom." This is the native word, now largely superseded by bloom (n.1) from Old Norse and flower (n.) from French.
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*bhel- (3)
Proto-Indo-European root meaning "to thrive, bloom," possibly a variant of PIE root *bhel- (2) "to blow, swell."

It forms all or part of: blade; bleed; bless; blood; blow (v.2) "to bloom, blossom;" bloom (n.1) "blossom of a plant;" bloom (n.2) "rough mass of wrought iron;" blossom; cauliflower; chervil; cinquefoil; deflower; defoliation; effloresce; exfoliate; feuilleton; flora; floral; floret; florid; florin; florist; flour; flourish; flower; foil (n.) "very thin sheet of metal;" foliage; folio; folium; gillyflower; Phyllis; phyllo-; portfolio; trefoil.

It is the hypothetical source of/evidence for its existence is provided by: Greek phyllon "leaf;" Latin flos "flower," folio, folium "leaf;" Middle Irish blath, Welsh blawd "blossom, flower;" Gaelic bile "leaflet, blossom;" Old English blowan "to flower, bloom."
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bloomers (n.)

1851, named for U.S. feminist reformer Amelia Jenks Bloomer (1818-1894), who promoted them. The surname is attested from c. 1200, said to mean "iron-worker," from Old English bloma (see bloom (n.2)). The original Bloomer costume was a short skirt, loose trousers buttoned round the ankle, and a broad-brimmed, low-crowned hat.

The failure of the Bloomer dress seems to have arisen from the mixed character it assumed, and the unpleasant confusion of ideas it occasioned. It partook of the man's the woman's and the child's. A bold assumption of a full male dress, as by Madame Dudevant and Miss Weber, and such as is worn at pleasure by ladies, traveling or on excursions, anywhere on the continent of Europe, would have had a much better chance of tolerance and success. ["The Illustrated Manners Book, A Manual of Good Behavior and Polite Accomplishment," New York, 1855]
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florescent (adj.)
"bursting into bloom," 1784, from Latin florescentem, present participle of florescere "to begin to bloom" (see florescence).
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