Timorousness is the noun from timorous: the quality of being easily frightened and having no confidence. It is the rarest word in this family — noticeably formal and a little heavy in the mouth, and you will meet it mostly in essays, criticism, and older prose. Two uses: a person's fearful nature ('his lifelong timorousness'), and, more often in modern writing, the over-cautiousness of a group or a plan ('the timorousness of the committee', 'the timorousness of the film's ending'), where it is a criticism. It is uncountable — no 'a timorousness', no plural. In practice most writers choose 'timidity' instead: same meaning, shorter, and far more common. Keep timorousness for when you have already used 'timorous' nearby and want the noun to match it, or when you want the sentence to sound deliberately formal.

膽怯、怯懦（名詞，非常書面；一般寫 timidity 就好）。