Unable and Wishy-washy

Unable adjective - Lacking qualities (as knowledge, skill, or ability) required to do a job.

Wishy-washy and unable are semantically related. In some cases you can use "Wishy-washy" instead an adjective "Unable".

Wishy-washy adjective - Lacking in qualities that make for spirit and character.

Unable and wishy-washy are semantically related. Sometimes you can use "Unable" instead an adjective phrase "Wishy-washy".