Ef

“Now ef ye alls don’t quit fussin’, I’ll set the boogers arter ye ter-night,” which was a dire and telling threat, for, to the mountain children, “boogers” meant ghosts, witches, hobgoblins, thieves, or any other terrible, mysterious creature of the night.

Source: tatoeba (11715144)

Ef was probably a bilabial, not a labiodental spirant, as is also evident from Goth.

Source: tatoeba (11916791)

I have drunk en-ee-cee-tee-ay-ar from the ef-ell-oh-doubleyou-ee-ar-ess in his gee-ay-ar-dee-ee-en many a time.

Source: wiktionary

Captain Tom would have hired him to hunt down his own child, ef Rosebud hadn’t interfered.

Source: wiktionary