adverb taking the 'to' particle, adverb
Describes a person or thing that is slender and somewhat unsteady-looking, often with a nuance of being gangly or weak. Used adverbially with と or as an adverbial modifier.
彼はひょろりと背が高い。
He is tall and lanky.
ひょろりとした若者が立っていた。
A spindly young man was standing there.
Mimetic word; the exact derivation is uncertain, but it is likely sound-symbolic, evoking a thin, swaying appearance.