Impromptu and Throwaway

Impromptu adjective - Made or done without previous thought or preparation.

Throwaway and impromptu are semantically related In some cases you can use "Throwaway" instead an adjective "Impromptu".

Throwaway adjective - Intended to be thrown away after use.

Impromptu and throwaway are semantically related in ad-lib topic. Sometimes you can use "Impromptu" instead an adjective "Throwaway", if it concerns topics such as temporarily helping.