s. 1. (in prosody) A long vowel-letter ا, included in the rhyme of a verse in such manner that between it and the rhyming letter, there is but one letter. 2. (rhetoric) A word such that, if omitted, its sense would not be indicated, (in distinction from a word used simply to corroborate another word). 3. (pl. تأسیسات) (astrology) Any one of the critical or unlucky points; i. e., the 12th 45th 90th 130th 138th 222d, 230th , 270th, 315th, or 348th degree; of the moon’s orbit, reckoned from the point of true conjuction.