Compare deponent verbs, which are passive in form and active in meaning.
From the en.wikipedia.org
Present deponent will testify no further as to the plot.
From the time.com
The synthetic verbs also have periphrastic forms, for use in perfects and in simple tenses in which they are deponent.
From the en.wikipedia.org
The imperative present of the passive voice is rarely used, except in the case of deponent verbs, whose passive forms carry active meaning.
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In linguistics, a deponent verb is a verb that is active in meaning but takes its form from a different voice, most commonly the middle or passive.
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Some verbs are deponent universally, but other verbs are deponent only in certain tenses, or use deponent forms from different voices in different tenses.
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Because Latin had no middle voice, Medieval Latin expresses such sentences by putting the verb in the passive voice, in a similar way to Latin deponent verbs.
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My understanding is that if syllabus is allowed to be imported into Latin, it is a deponent second declension, therefore neuter in the plural, not masculine.
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Deponent verbs are typically passive in form but active in meaning and their participles thus take the form but not the meaning of the perfect passive participle.
From the en.wikipedia.org
More examples
Testifier: a person who testifies or gives a deposition
A witness; especially one who gives information under oath, in a deposition concerning facts known to him or her; A deponent verb; Having passive form (that is, conjugating like the passive voice), but an active meaning. ...
A witness; an affiant.
One who testifies under oath to the truth of facts.
A person making a statement under oath or affirmation, often in an affidavit.
A word describing the phenomenon of a verb setting aside some or nearly all of its active forms and translating the remaining passive forms as if they were active. ...
A person who makes (deposes to) an affidavit.
A person who testifies, especially in writing, under oath. The person answers questions put to him and these questions and his answers are recorded in shorthand by the court reporter. ...
Person who, under oath or affirmation, gives oral testimony that is transcribed for use in a legal proceeding.