thin space

Noun

thin space (plural thin spaces)

1. A metal block used to separate words, one fifth of an em in width.
   • If it be only a Single Letter or two that drops, he thruſts the end of his Bodkin between every Letter of that Word, till he comes to a Space: and then perhaps by forcing thoſe Letters closer, he may have room to put in another Space or a Thin Space; which if he cannot do, and he finds the Space...1683, Joseph Moxon, Mechanick Exercises: Or, the Doctrine of Handy-Works. Applied to the art of Printing., volume 2, pages 240–41

   Synonyms:

   5-to-the-em space, 5-em space

2. In digital text, a character representing a thin space.
   • All you may see on the keyboard is a space bar, but typographers use several invisible characters: the word space, fixed spaces of various sizes (em space, en space, thin space, figure space, etc) and a hard space or no-break space.2002, Robert Bringhurst, The Elements of Typographic Style (version 2.5), Vancouver, Hartley & Marks, p 43

   Synonyms:

   5-to-the-em space, 5-em space