Bombast, rhapsody, rant, fustian, rodomontade all designate a style of speech or writing characterized by high-flown pomposity or pretentiousness of language disproportionate to the thought or subject matter.
All of them are derogatory in some degree; some of them are frankly contemptuous.
Bombast does not necessarily connote emptiness of thought, but it implies inflation or a grandiosity or impressiveness in language and style which so outruns the thought that the attention is distracted from the matter and concentrated upon the manner of expression.
When used in description rather than in censure, bombast often additionally suggests a soaring eloquence or a kind of oratorical grandeur, such as is found in Marlowe’s Tamburlaine the Great or is characteristic of Elizabethan drama in comparison with modern realistic drama; when used in depreciation, it suggests padding, windiness, verbosity, and exaggeration.
Rhapsody, like bombast, may be scarcely or obviously derogatory. It designates an ecstatic or effusive utterance or writing in which the language or style is governed by the feelings rather than by logical thought. It may, at one extreme, suggest inspired utterance (as in rapture) or, at the other, a maudlin loquaciousness.
In scholarly and critical use it is often applied to a kind of writing that has no perceptible argument and is seemingly incoherent, yet moves by a kind of logic of its own from one expression of feeling or one image to another.
Rant and fustian are definitely terms of derogation. Both are applicable to bombast and rhapsody at their worst, but rant stresses its extravagance or violence of expression or utterance and fustian the banality of its quality or the preposterousness of its character.
Rodomontade is applied especially to the rant of the braggart, of the demagogue, or of anyone given to bluster and magniloquence.