Yes, it is a form of the verb "to overhear" (to hear part of another conversation). It is the past tense and past participle of the verb, and may be used as an adjective (e.g. overheard secrets).
Yes, "whisper" is a verb. It is an action performed when speaking quietly in a hushed or soft voice to avoid being overheard.
Yes it is a verb because a verb is a doing word, so there is some action involved therefore it is a verb.
An antonym for overheard could be overlooked or ignored.
The teacher turned on the overhead for her class to copy the notes.
My joyful thankfulness to the puppy for his successful fetching of the newspaper was rewarded the next day with eight newspapers!
To overhear someone or something means to hear speech between others. Overheard is the preterite and past participle of that verb."I overheard 'em! They're plotting to rob a bank."
Yes, it is one word, the verb or adjective overheard.
The word "sense" can be used as a verb. Here's an example:"I sense that he might have overheard us making plans."
Yes, "whisper" is a verb. It is an action performed when speaking quietly in a hushed or soft voice to avoid being overheard.
Yes it is a verb because a verb is a doing word, so there is some action involved therefore it is a verb.
Overheard
An antonym for overheard could be overlooked or ignored.
The duration of Overheard - film - is 1.65 hours.
Overheard - film - was created on 2009-07-30.
I was scared when I overheard my mum and dad arguing.
The couple whispered as they did not want to be overheard by the people sitting at the next table.
Synonyms for the word overheard: discovered, heard, recorded