cowardly — If you describe someone as cowardly, you disapprove of them because they are easily frightened and avoid doing dangerous and difficult things.
invertebrate — Zoology. not vertebrate; without a backbone. of or relating to creatures without a backbone.
submissive — inclined or ready to submit or yield to the authority of another; unresistingly or humbly obedient: submissive servants.
timid — lacking in self-assurance, courage, or bravery; easily alarmed; timorous; shy.
vacillating — not resolute; wavering; indecisive; hesitating: an ineffectual, vacillating person.
weak — not strong; liable to yield, break, or collapse under pressure or strain; fragile; frail: a weak fortress; a weak spot in armor.
weak-kneed — yielding readily to opposition, pressure, intimidation, etc.
weak-willed — having or showing a want of firmness of will; easily swayed.
yellow — a color like that of egg yolk, ripe lemons, etc.; the primary color between green and orange in the visible spectrum, an effect of light with a wavelength between 570 and 590 nm.