Saad
The emphatic /s/ — heavier and darker than seen, and a colourer of the vowels around it.
Sound
Saad is /sˤ/, an emphatic /s/. The articulation in front is the same as seen — tongue blade approaches the alveolar ridge, air hisses through — but the back of the tongue retracts toward the pharynx, the body of the tongue bunches up, and the whole shape of the vocal tract changes. The acoustic result is a "darker," "fuller," lower-pitched /s/ than seen.
The most reliable cue, both in producing and in hearing Saad, is what happens to neighbouring vowels. An a next to Saad sounds more like the a in father — back, dark, open — while the same a next to seen sits forward and bright, closer to the a in cat drawn out. Native listeners use vowel quality as much as the consonant itself to tell the two letters apart.
For English speakers Saad is hard to fake. Producing it as an ordinary /s/ is a clearly marked foreign accent — not unintelligible, but immediately audible. The only way to acquire it is to listen to and imitate native speakers. Saad is one of the four "emphatic" consonants of the alphabet, alongside Daad, Taa, and Zaa. It is stable across dialects.
Forms
Connecting behavior
Saad is a normal two-sided connector. The shape is built around a closed loop on the right and a small notch or curve on the left; in initial and medial positions the form continues into a connected baseline, while isolated and final forms close with a downward tail.
Easy to confuse with
Saad shares its skeleton with one letter only: Daad (ض), distinguished by a single dot above. The dotless one is Saad. There is no other letter close in shape, so once you have learned the loop-with-notch you have learned Saad.
Examples in common words
A note on handwriting
The closed loop on the right is the distinguishing feature of Saad and must remain a loop in handwriting — flattening it into a horizontal line turns the shape into something seen-like, which is then unreadable. Writers usually draw the loop in a single round motion before continuing into the rest of the letter. The notch on the left, where in print there is a small dip before the final tail, is often softened into a smooth curve. The dot above (which would indicate Daad) must not be added.