Demolish is a verb.
Demolished is a verb (past tense of demolish) and an adjective (a demolished building).
demolish = a demola
'Prepare' is not the opposite of 'demolish'; 'build' or 'construct' are two words that are opposites of 'demolish'.
A homonym is a word that sounds identical to another word in speech, but has a different meaning. For example, "two" and "too". One is a number, the other means "also". (This example is specifically a "homophone", but there is another kind of homonym called a "homograph", where the word looks the same but is not necessarily pronounced the same and means differently.) "Demolish" only has one meaning/word/sound. It doesn't have a homonym.
The part of speech for this particular word is a noun.
part of speech
The part of speech for "answer" is a noun.
what part of speech is beneath
adverb
The man had to demolish the car in thirty seconds.
The part of speech for "explicit" is an adjective.
The part of speech for "lecturer" is a noun.