Adjective

(en adjective)

Having a strong tendency to change.

* {{quote-magazine, date=2013-08-03, volume=408, issue=8847, magazine=(The Economist)

, title= Yesterday’s fuel , passage=The dawn of the oil age was fairly recent. Although the stuff was used to waterproof boats in the Middle East 6,000 years ago, extracting it in earnest began only in 1859 after an oil strike in Pennsylvania.

Fluctuating; not constant.

Fickle.

Unpredictable.

(chemistry) Readily decomposable.

(physics) Radioactive, especially with a short half-life.

Adjective

(er)

Dizzy, feeling dizzy or unsteady and as if about to fall down.

The man became giddy upon standing up so fast.

Causing dizziness: causing dizziness or a feeling of unsteadiness.

They climbed to a giddy height.

Lightheartedly silly, or joyfully elated.

* {{quote-book, year=1905, author=

, title= , chapter=2 citation , passage=Miss Phyllis Morgan, as the hapless heroine dressed in the shabbiest of clothes, appears in the midst of a gay and giddy throng; she apostrophises all and sundry there, including the villain, and has a magnificent scene which always brings down the house, and nightly adds to her histrionic laurels.}}

The boy was giddy when he opened his birthday presents.

(archaic) Frivolous, impulsive, inconsistent, changeable.

* 1599 ,

In brief, since I do purpose to marry, I will think nothing to any purpose that the world can say against it; and therefore never flout at me for what I have said against it, for man is a giddy thing, and this is my conclusion.

* 1784 , , Tirocinium; or, A Review of Schools

Young heads are giddy and young hearts are warm,

And make mistakes for manhood to reform.