bloom (n.1) Look up bloom at
"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 (cognates: Old Saxon blomo, Middle Dutch bloeme, Dutch bloem, Old High German bluomo, German Blume, Gothic bloma), from PIE *bhle- (cognates: Old Irish blath "blossom, flower," Latin flos "flower," florere "to blossom, flourish"), extended form of root *bhel- (3) "to thrive, bloom" (see folio). Related to Old English blowan "to flower" (see blow (v.2)).

Transferred sense, of persons, 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).
bloom (n.2) Look up bloom at
"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.
bloom (v.) Look up bloom at
mid-13c., blomen, from the noun (see bloom (n.1)). Related: Bloomed; blooming.