Lecture, oration, redress.
address
Another word for a formal speech is an oration or a discourse.
Formal is an adjective.
stutter stammer
The starting word of a speech is the introduction. Many people begin their speech with a greeting to the audience and distinguished guests.
A casual word that is often avoided in formal speech or writing is "gonna," a contraction of "going to." It's better to use the full phrase in formal settings.
I'm not sure whether you are asking about "formal" (which is an adjective) or "in" (which is a preposition).
a harfo
A four letter word starting with the letter a is able.
Formal
The word whomever is a pronoun. It is the formal usage of whoever.
H is a letter, not a word. To be a part of speech, it needs to be a word.
Waterhose is a nine letter word starting with the letter W!