flimsy
flim-sy
adjective
Thin, easily broken or damaged; lacking strength, substance, or credibility.
"Her flimsy excuse was unconvincing."
Thesaurus
Synonyms: unconvincing, unpersuasive, weak, insubstantial, onionskin, insignificant, slight, unimportant, fragile, tenuous, thin
Antonyms: convincing