instil
Pronunciation: /ɪnˈstɪl/
(also instill)
verb ( instils, instilling, instilled)

Origin:
late Middle English (in instil (sense 2)): from Latin instillare, from in- 'into' + stillare 'to drop' (from stilla 'a drop')

Spelling rule
Double the l when adding endings which begin with a vowel to words which end in a vowel plus l (as in travel):