epenthesis

1. The addition of a letter, sound, or syllable to the middle of a word. A kind of metaplasm. (Silva Rhetoricae)

2. Interposition; it is the interposition of a letter or syllable in the middle of a word.; Epenthesis, interpositio, interposition, or a putting in between. Epenthesis is the interposition of a letter or syllable in the midst of a word. (JG Smith)

3. Epenthesis, or Insertion, is our next figure of etymology, the inserting of a letter or letters in the middle of a word. (Macbeth)

4. Epenthesis to th' middle adds one more, Than what the word could justly claim before. (Holmes)

1. Addition of a medial letter:

When "sherbet" is pronounced "sherbert"

Addition of an medial syllable:

When "realtor" is pronounced "realator"

I have but with a cursorary eye O'erglanc'd the articles.
—Shakespeare, Henry V 5.2.77 (Silva Rhetoricae)

3. "I du believe in prayer and praise
To him-that hez the grantin'
Of jobs; in every thing that pays;
But most of all in cantin' ;
That doth my cup with marcies fill,
That lays all thought o' sin to rest;
I don't believe in Princerple,
But, oh! I du in Interest."
- James Russell Lowell (Macbeth)

4. Blackamoore, for Blackmoor. (Holmes)