٢- قاعدة عِدَة

If

• masdar is on the scale of فِعْلٌ 
• faa kalimah is a و

then

• delete waw
• give ayn kalimah a kasra
• add ة at the end of the word

Example:

وَعْدٌ

——>

عِدَةٌ

Note:

If 

• mudari has fatha on ayn kalimah

then 

• faa kalimah of masdar can be given a fatha

Example:

وِسْعٌ

——>

سَعَةٌ