Verbs with a weak middle radical are those which have ᵓalif (.. ا..) as the middle radical of the basic verb form. This middle ᵓalif (ا) is derived from the weak radical https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2089.tif"/> /w/ or https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2090.tif"/> /y/. These types of verbs are also called 'hollow' https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2091.tif"/> because their original middle radical is lost in the basic (and many other) verb forms, e.g.:

https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2092.tif"/> qāla, to say (for: https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2092a.tif"/> qawala) from the root https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2092b.tif"/> qwl

https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2093.tif"/> bāˤa, to sell (for: https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2093a.tif"/> bayaˤa) from the root https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315620091/1e85dcd9-67fa-4282-a164-2a1659972fa7/content/inline2093b.tif"/> byˤ