skittish

Easily scared or startled; timid.

The dog likes people he knows, but he is skittish around strangers.

1557, Roger Edgeworth, Sermons Very Fruitfull, Godly, and Learned, London: Robert Caly, The fiftenth treatice or Sermon, All such be like a skittish starting horse, whiche coming ouer a bridge, wil start for a shadowe, or for a stone lying by him, and leapeth ouer on the other side into the water, & drowneth both horse and man.

Wanton; changeable; fickle.

How some men creep in skittish fortune’s hall, Whiles others play the idiots in her eyes!

[…] ’Tis pitiful To court a grin, when you should wooe a soul; To break a jest, when pity would inspire Pathetic exhortation; and t’ address The skittish fancy with facetious tales, When sent with God’s commission to the heart.

Difficult to manage; tricky.

For everybody’s family doctor was remarkably clever, and was understood to have immeasurable skill in the management and training of the most skittish or vicious diseases.