Eyelid batting
The other day a friend asked me about the origins of the phrase “to bat an eyelid”, which is normally used in the negative – he didn’t bat an eyelid at the pink elephant in the fridge – and means that you don’t react or show emotion when surprised or shocked. Or in other words, you took it in your stride. We wondered way it’s ‘bat’, which seems a strange thing to do with your eyelids.
The same verb is used in the phrase “to bat ones eyes/eyelashes”, meaning to open and close your eyes very quickly several times, intending to be attractive to someone [source].
According to the OED, the verb to bat is a variant of bate (to flutter as a hawk), from the Old French batre (to contend, fight, strive, flutter), from the late Latin batĕre/battĕre, from the classical Latin batuĕre (to hit, beat, pound). This comes from the Proto-Indo-European prefix bhau- (to hit) [source], which is also the root of such English words as butt and batter.
A lot more words are related: see http://www.utexas.edu/cola/centers/lrc/ielex/X/P0197.html
Including beetle, buttock, button, footle, hobbit, rebut and refute,. In Italian we also get: futuo, futuere, futui, futūtumto “have intercourse”.
Maybe the old people at that time imagined the act of blinking as .. the eyelids batting (hitting) each other.
What do butts have to do with hitting?
It’s the root of to butt, as in to strike or push with the head or horns, not butt(ocks).