The repeating of beginning consonant sounds is called aliteration.
good
pear
noon deed
Plumkin is a made-up word that rhymes with pumpkin and starts with the P sound.
echo
It is called a homophone. Homophones are words that sound the same when pronounced, but have different meanings and often different spellings.
Use "a" before a word that starts with a consonant sound, and use "an" before a word that starts with a vowel sound. For example, "a cat" (pronounced as kæt) and "an apple" (pronounced as əˈpl̩). Remember that it is based on the sound, not the actual letter.
That word is 'one'
Words that have the same sound are called "homophones", or if spelled the same, "homonyms".
cosine?
Both "an historian" and "a historian" are correct, but generally "a historian" is more commonly used. The use of "an historian" follows British English rules of using "an" before words that begin with a silent 'h'.
an hour An hour. The rule is, use a if the next word following it starts with a consonant sound. Use an if it starts with a vowel sound. Since in the word hour, the h is silent, that means it actually starts with the sound of the o, a vowel.