Meaning: Behave in a free or uninhibited manner.
Background:
Letting one's hair down was a commonplace part of womens' daily activities in
the 17th century. The hair was normally pinned up and was let down for
brushing or washing. The term used for this at the time was dishevelling.
Anyone who is unkempt and generally untidy might now be described as
dishevelled but then it applied specifically to hair which was unpinned. The
first reference I can find which refers specifically to this is John
Cotgrave's, The English treasury of wit and language, 1655:
"Descheveler, to discheuell; to pull the haire about the eares."
- www.phrases.org.uk [edited]
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Knowing the background of this phrase, I wondered if it applies only to women
and at that only those with long hair done up. AI said it's for everyone and
that's a relief. "Let one's guard down" comes close.
