full-blown (adj.) Look up full-blown at Dictionary.com
1640s, of flowers, from full (adj.) + past participle of blow (v.2) "to bloom." Figuratively "complete, fully developed" from 1650s. Blown "that has blossomed" is from Old English geblowenne. Full-blown also was used 17c.-18c. of cheeks, sails, bladders and in this case is from blow (v.1) and the figurative sense might also partake of these.