ʿAyn
The voiced pharyngeal fricative — probably Arabic's most distinctive consonant.
Sound
ʿAyn is /ʕ/, a voiced pharyngeal fricative. There is no equivalent in English. The closest mental model: imagine the constricted, voiced sound that comes out when a doctor presses on the back of your tongue with a depressor — a sustained, slightly strained sound from deep in the throat, with vocal cords vibrating. The constriction is in the pharynx, well behind where any English consonant lives.
It is probably the single most distinctive Arabic consonant. Mispronouncing it as a vowel, dropping it, or replacing it with a glottal stop are all very marked foreign-accent moves. Native listeners hear the omission immediately — the word will not sound like the word.
The most reliable way for an English speaker to start producing ʿayn is to begin with a long /a/, then squeeze the throat at the bottom (not the back of the mouth) until the sound is clearly constricted but still voiced. Done right, you can sustain it. Done wrong, it either becomes a vowel (no constriction) or a glottal stop (closure rather than fricative).
Forms
Connecting behavior
ʿAyn connects on both sides. The four positional forms look quite different from one another — the medial form in particular (a small triangular wedge above the line) bears little obvious resemblance to the open, curl-and-tail isolated form.
Easy to confuse with
Ghayn (غ). ʿAyn and ghayn share the same skeleton in all four positions. The dot above is ghayn; no dot is ʿayn. As with the other dot-distinguished pairs, the dot is the entire visual signal.
Examples in common words
A note on handwriting
ʿAyn's curve-and-tail in isolated and final position is one of the more recognizable shapes in Arabic handwriting. The medial form, the small triangular notch sitting on the connecting line, is drawn in a single down-up motion. Beginners often draw it too tall or too pointed; in mature hands it is short and rounded.