Shaddah (Arabic: shaddah "[sign of] emphasis", also called by the verbal noun from the same root, tashdid tashd?d "emphasis") is one of the diacritics used with the Arabic alphabet, marking a long consonant (geminate). It is functionally equivalent to writing a consonant twice in the orthographies of languages like Latin, Italian, Swedish, and Ancient Greek, and is thus rendered in Latin script in most schemes of Arabic transliteration, e.g. = rumm?n 'pomegranates'.
When a shaddah is used on a consonant which also takes a fat?ah /a/, the fat?ah is written above the shaddah. If the consonant takes a kasrah /i/, it is written between the consonant and the shaddah instead of its usual place below the consonant.
For example, see the location of the diacritics on the letter h in the following words:
|Arabic||Transliteration||Meaning||Diacritic||Location of the diacritic|
|yafhamu||he understands||fat?ah||Above the letter|
|?||fahhama||he explained||fat?ah||Above the shaddah|
|fahima||he understood||kasrah||Below the letter|
|?||fahhim||explain!||kasrah||Between the shaddah and the letter|
Consonant length in Arabic is contrastive: darasa means "he studied", while ? darrasa means "he taught"; ? ? bak? ?abiyy means "a youth cried" while ? bakk? ?-?abiyy means "a youth was made to cry".
A consonant may be long because of the form of the noun or verb; e.g., the causative form of the verb requires the second consonant of the root to be long, as in darrasa above, or by assimilation of consonants, for example the l- of the Arabic definite article al- assimilates to all dental consonants, e.g. () (a)?-?abiyy instead of (a)l-?abiyy, or through metathesis, the switching of sounds, for example aqall 'less, fewer' (instead of *? aqlal), as compared to ? akbar 'greater'.
A syllable closed by a long consonant is made a long syllable. This affects both stress and prosody. Stress falls on the first long syllable from the end of the word, hence aqáll (or, with i?r?b, aqállu) as opposed to ? ákbar, ? ma?ábbah "love, agape" as opposed to ma?rifah '(experiential) knowledge'. In Arabic verse, when scanning the meter, a syllable closed by a long consonant is counted as long, just like any other syllable closed by a consonant or a syllable ending in a long vowel: ? a-l? tamda?anna 'Will you not indeed praise...?' is scanned as a-l? tam-da-?an-na: short, long, long, short, long, short.