Giggle

VERB

1. to laugh lightly in a nervous, affected, or silly manner (Google)
2. to laugh in a nervous or childlike way (Merriam-Webster)
3. to laugh with repeated short catches of the breath (Merriam-Webster)
4. to laugh gently or in a high-pitched voice; to laugh in a silly or giddy way (Wiktionary)

NOUN

1. a light, silly laugh  (Google)
2. a silly, spasmodic laugh; titter (Dictionary.com)
3. A high-pitched, silly laugh (Wiktionary)