long i

Short definition from Wiktionary

Noun

1. 1
   the English vowel sound /aɪ/ in the words "fine" and "like", conventionally written ⟨ī⟩.
2. 2
   a tall variant of the letter i, ⟨ꟾ⟩, used in all-capital Latin inscriptions and manuscripts in classical antiquity and the Early Middle Ages for a long vowel /iː/. (Other long vowels were marked with apices.)