Unassertive and Up on

Unassertive adjective - Inclined to timidity or lack of self-confidence.

Up on and unassertive are semantically related. In some cases you can use "Up on" instead an adjective "Unassertive".

Up on adjective - Being up to particular standard or level especially in being up to date in knowledge.

Unassertive and up on are semantically related. Sometimes you can use "Unassertive" instead an adjective "Up on".