This is the 9835th most frequent Portuguese word.
desaparecerem
"Desaparecerem" means "to disappear" (in the third-person plural subjunctive or future form).
In this sentence, 'desaparecerem' is used as an infinitive verb in a subjunctive construction, expressing necessity.
Os objetos precisam desaparecerem antes que alguém veja.
The objects need to disappear before anyone sees them.
Here, 'desaparecerem' appears in the subjunctive tense, used in conditional clauses.
Se eles desaparecerem, chamaremos a polícia.
If they disappear, we will call the police.
Although not in the infinitive itself, this clarifies 'desaparecer': it's a verb expressing hopeful action in subjunctive.