Roar, bellow, bluster, bawl, vociferate, clamor, howl, ululate are comparable when they mean to make a very loud and often a continuous or protracted noise.
The same distinctions in implications and connotations are to be found in their nouns, all of which are identical in spelling with the corresponding verbs except vociferation and ululation.
Roar implies such a heavy, hoarse, and prolonged sound as is made by the booming sea, by thunder that reverberates, by a lion, or by persons when they lose control (as in rage or in boisterous merriment).
Bellow suggests the loud, hollow crying of a bull; by extension, it applies to sound that seems to reverberate loudly from a cavity or to come insistently from a distance.
Bluster suggests not only the violence or turbulence of a windstorm but the lashing quality of its blasts. It is applicable not only to violent weather but also to something (as loud boastful swaggering or empty but noisy threats or protests) that suggests such weather. The term in extended use often carries a connotation of useless or futile effort.
Bawl is sometimes interchangeable with bellow, but typically it suggests less depth and resonance and more persistence. As applied to human utterance, bawl is more or less derogatory.
Even when applied specifically to unrestrained weeping and wailing it tends to call up an unsympathetic image of dishevelment and disorder.
Vociferate and vociferation, like bawl, imply loud and urgent human utterance, but they are far less derogatory, if derogatory at all, more adapted to writing than to speech, and more likely to suggest a reason (as rage or excitement), a call for help, or a protest, than mere temperament.
Clamor implies, usually, loud noises in confusion; it may suggest a mingling of voices or sounds. The term can apply to loud sounds, whatever their source. As applied to human utterances, it commonly gains the suggestion of vehemence (as in insisting, urging, or protesting).
Howl often stresses such loudness and mournfulness as is characteristic of the protracted cry of dogs and wolves; it may be used not only of animals but also of persons or things that make doleful or agonized and often prolonged sounds.
Especially when used of human utterance, howl may suggest not only the quality of the sound but the unrestrained character of the utterance or of its underlying emotion.
Ululate and ululation are less common and more literary than howl, from which they differ chiefly in carrying less suggestion of unrestrained emotion and a stronger implication of wailing, often giving a hint of the peculiar rhythm of the sounds.