1. extra extra extra small - Noun
2. extra extra extra small - Adjective
(countable) An item labelled or denoted as being that size.
(countable) One who fits an item of that size.
(uncountable) One of several sizes to which an item may be manufactured.
Synonym: XXXS
(especially clothing) That is extra extra extra small (the manufactured size).
Used other than figuratively or idiomatically: see extra, small.
Source: en.wiktionary.org