請問多音節的英文單字(形容詞)有什麼呢?(請舉例5個以上)那不規則的又有什麼呢?

Multi-syllable word 多音節的英文單字 is a word that has more than one syllable. For adjectives with multi-syllable, you usually can’t just add ‘er’ or ‘est’ to the end of them to form the comparative and superlative forms.

Example:
expensive → more expensive → most expensive
beautiful → more beautiful → most beautiful
difficult → more difficult → most difficult
horrible → more horrible → most horrible
ridiculous → more ridiculous → most ridiculous

Irregular adjectives:
A small number of adjectives are irregular in the way they make comparative and superlative forms NOT just by adding -er/-est or using more/most.

Example:
good → better → the best
bad → worse → the worst
far → further → the furthest
old → elder → the eldest
little → less → the least
much → more → the most
excellent → excellent → excellent (there is no comparative and superlative forms for "excellent", "perfect", etc.)

Syllable is rhythmic unit of spoken, similar unit of written of words, consisting of a vowel or sustained or unsustained consonant
The many phonetic syllables of the irregular past tense and past participles forms of 5 English words having a stated number of syllables as declared by your posting are given:-
Infinitive---------Past tense-----------Past Participle
broadcast-------broadcasted---------broadcasted,
forbid-------------forbade---------------forbidden,
misunderstand-misunderstood-----misunderstood,
rewrite------------rewrote---------------rewritten,
undertake--------understood----------undertaken,
Do you want 5 longest words in spelling in English ?