فَعَّالٌ-intensive

Intensive Noun/ الْاِسْمُ الْمُبَالَغَةُ 

From verbal adjectives of the form فَاعِلٌ as well as from some others, is derived an adjective فَعَّالٌ which adds intensiveness or habit to the basic meaning hence it is called the noun of intensiveness / اِسْمُ المُبَالَغَةِ 

The nouns which indicate professions and trades usually have this form