From Latin 'in-' (not) + 'gnōrāre' (to know), from PIE *ǵneh₃- — the direct negation of the root for knowledge.
Lacking knowledge or awareness in general or about a particular subject; uninformed.
From Old French 'ignorant,' from Latin 'ignōrantem' (nominative 'ignōrāns'), present participle of 'ignōrāre' (to not know, to be unaware of, to disregard), formed from 'in-' (not) + Old Latin 'gnōrāre' (to know, to become acquainted with), from 'gnārus' (knowing, expert), from PIE *ǵneh₃- (to know, to recognise). This PIE root is one of the most prolific in the Indo-European family: it produced Greek 'gignōskein' (to know) and 'gnōsis' (knowledge), Latin '(co)gnōscere' (to learn), 'nōbilis' (knowable, notable — whence 'noble'), 'nōtiō' (a concept), Sanskrit 'jñā-' (to know), and English 'know' itself via Proto-Germanic *knēaną. The word 'ignorant' is thus literally 'un-knowing' — formed by negating the very root of knowledge
The initial 'gn-' of Latin 'gnōrāre' was lost in Classical Latin, yielding 'ignōrāre' rather than the expected '*ingnōrāre.' The same loss happened across the board: 'gnōbilis' (knowable, notable) became 'nōbilis' (noble), and 'gnōscere' became 'nōscere' (to come to know). But the 'g' was preserved in Greek cognates like 'gnōsis' and 'gnōrizein,' showing that the original PIE root began with *ǵ-.