creepmouse

Etymology
, from a likening of a person's character and/or behaviour to that of a small, timorous, and often unseen rodent.

Adjective

 * 1)  Timid and unassuming in the extreme.

Noun

 * 1)  An extremely timid and unassuming person.
 * 2) * 1831, Catherine Gore, Mothers and Daughters, Volume II, E. L. Carey & A. Hart/Allen & Ticknor (1834), page 62:
 * "Pho! pho ! — I do not believe a word of it. Lord Basingstoke is one of those shy young men who are very much attached to any one who will take the trouble of making love to them ; — one of those creepmice who run away with their mother's waiting-maid, or marry an actress for want of courage and patience to encounter the formalities of an honourable courtship.