Roundel

A roundel in heraldry is any circular shape; in military use it is an emblem of nationality employed on military aircraft and air force flags, generally round and consisting of concentric rings of different colors.
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Noun
1. English form of rondeau having three triplets with a refrain after the first and third
(hypernym) rondeau, rondel
2. round piece of armor plate that protects the armpit
(hypernym) armor plate, armour plate, armor plating, plate armor, plate armour
(part-holonym) body armor, body armour, suit of armor, suit of armour, coat of mail, cataphract
3. a charge in the shape of a circle; a hollow roundel
(synonym) annulet
(hypernym) charge, bearing, heraldic bearing, armorial bearing

(a.)
Anything having a round form; a round figure; a circle.
  

(a.)
A small circular shield, sometimes not more than a foot in diameter, used by soldiers in the fourteenth and fifteenth centuries.
  

(a.)
A rondelay.
  

(a.)
A circular spot; a sharge in the form of a small circle.
  

(a.)
A bastion of a circular form.
  

The round metal attachment at the base of a polearm to keep the hands from sliding down the shaft and onto the blade, where they might be harmed.

Synonyms and related words:
English sonnet, Horatian ode, Italian sonnet, O, Petrarchan sonnet, Pindaric ode, Sapphic ode, Shakespearean sonnet, alba, anacreontic, annular muscle, annulus, areola, aureole, balada, ballad, ballade, bucolic, canso, chanson, chaplet, circle, circuit, circumference, circus, clerihew, closed circle, corona, coronet, crown, cycle, diadem, dirge, discus, disk, dithyramb, eclogue, elegy, epic, epigram, epithalamium, epode, epopee, epopoeia, epos, eternal return, fairy ring, garland, georgic, ghazel, glory, haiku, halo, idyll, jingle, lasso, limerick, logical circle, loop, looplet, lyric, madrigal, magic circle, monody, narrative poem, noose, nursery rhyme, ode, orbit, palinode, pastoral, pastoral elegy, pastorela, pastourelle, poem, prothalamium, radius, rhyme, ring, rondeau, rondel, rondelle, round, roundelay, satire, saucer, sestina, sloka, song, sonnet, sonnet sequence, sphincter, tanka, tenso, tenzone, threnody, triolet, troubadour poem, verse, verselet, versicle, vicious circle, villanelle, virelay, wheel, wreath