Erelim is one of the rarest words in the Hebrew Bible. It appears at Isaiah 33:7, in a line most English versions render as their valiant ones shall cry outside, and it appears nowhere else in a form scholars agree on. The root suggests strength or heroism, which is where the usual gloss of valiant ones comes from, but the word is obscure enough that translators have reached for lion of God, for envoys and for messengers as well, and the Isaiah passage supplies no context that would settle the choice.
Later Jewish tradition took the word as a class of angels regardless. A well-known Talmudic passage on the death of Judah the Prince has the erelim and the mortals each taking hold of the ark of the covenant, with the angels prevailing, and by the time the ranked lists were being assembled the erelim were an established order rather than a disputed noun. That is the sequence worth noticing: the rank existed first as a name in liturgy and aggadah, and its systematic position was assigned to it afterwards.
It is also why the erelim have no fixed visual form, unlike the wheels of Ezekiel or the six-winged seraphim of Isaiah 6. There is no scene to draw. A rank whose only scriptural anchor is a single contested word carries a place in a hierarchy and very little else, and the honest course is to say so rather than to invent an emblem the tradition never used.