جَمْعُ التَّكْسِيرِ
1.
(assumed tropical:) [The broken plural;] the plural in which the composition of the singular is changed; (K;) the change being either apparent, as in رِجَالٌ, plural of رَجُلٌ, or understood, as in فُلْكٌ, which is both singular and plural, for the dammeh in the singular in this case is like the dammeh of قُفْلٌ, and that in the plural is like that of أسْدٌ. (Ibn- 'Akeel: see Dieterici's “ Alfijjah ” &c.; pp. 329 and 330.)
2.
Also تَكْسِيرٌ (assumed tropical:) [The area of a circle]: in the circle are three things: دَوْرٌ [or circumference] and قُطْرٌ [or diameter] and تَكْسِيرٌ [or area], which [last] is the product of the multiplication of the half of the
قطر
by the half of the
دور: and it is sometimes called مِسَاحَةٌ. You say, مَا تَكْسِيرُ دَايءِرَةٍ
قُطْرُهَا سَبْعَةٌ وَدَوْرُهَا اثْنَانِ وَعِشْرُونَ [What is the area of a circle of which the diameter is seven and its circumference two-and-twenty?]: and the answer is ثَمَانِيَةٌ وَثَلَاثُونَ وَنِصْفٌ [Eight-and-thirty and a half]. (TA.) [It is scarcely necessary to add that this is not perfectly exact.]