blazon n.

"armorial bearings, coat of arms," late 13c., from Old French blason (12c.) "a shield, blazon," also "collar bone;" a common Romanic word (compare Spanish blason, Italian blasone, Portuguese brasao, Provençal blezo, the first two said to be French loan-words) but one of uncertain origin. OED doubts, on grounds of sense, the connection proposed by 19c. French etymologists to Germanic words related to English blaze (n.1).

1560s, "to depict or paint (armorial bearings)," from blazon (n.) or else from French blasonner, from the noun in French. It was used earlier in English as "to set forth descriptively" (1510s); especially "to vaunt or boast" (1530s); in this use it is probably from or influenced by blaze (v.2).