I’d name a property like onClickListeners . The short version works great only for DSLs where you are defining your listiners “in place”. Usually, in a typical Kotlin DSL, the default behavior shoud be to add a new listener to the internal list, since that is consistent with how other DSL constructions typically work:

parent {
    child { … }
    child { … }
    onClick { … }
    onClick { … }
}