extra small

Short definition from Wiktionary

Noun

1. 1
   One of several sizes to which an item may be manufactured.
2. 2
   An item labelled or denoted as being that size.
3. 3
   One who fits an item of that size.
4. 4
   Alternative spelling of extra small.

Adjective

1. 1
   That is extra small (the manufactured size).
2. 2
   Used other than figuratively or idiomatically: see extra, small.
3. 3
   Alternative spelling of extra small.