Expresses a moderate degree or small amount. Can modify adjectives, verbs, or nouns. The 'a short time' nuance is less common and usually clear from context.
ちょっと is very casual and conversational; やや is more neutral and can be used in writing or polite speech.
Etymology
The origin is uncertain; it may be related to the classical adverb やや (meaning 'a little' or 'gradually'). The kanji forms 稍 and 漸 are rarely used in modern Japanese.
