Showy, pretentious, ostentatious can mean making or presenting an outward display that is by implication greater than what is necessary or justifiable.
Showy, the ordinary term, carries less definite implications than the other words. It implies an imposing, striking, or impressive appearance, but it often suggests cheapness, inferiority, or poor taste or undue conspicuousness or gaudiness or overattention to superficial qualities.
Pretentious (see also AMBITIOUS 2 ) suggests even less warrant for display, for it usually implies an appearance that is not justified by the thing’s actual value or actual cost or by the person’s actual worth, rank, performance, or capability; the term therefore implies a criticism of whatever is so described.
Ostentatious stresses vainglorious display or parade but it does not necessarily imply either showiness or pretentiousness.