The word 'apocalypse' in Greek means 'unveiling'.

True: standard Greek lexicons give 'uncovering', 'unveiling' or 'revelation' as the meaning of ἀποκάλυψις (from apo- 'off' + kalyptein 'to cover'). Mostly true: lexicons give 'revelation' or 'disclosure' as the main sense, with 'unveiling' only as the literal or etymological sense. Mostly false: 'unveiling' is only a remote or contested rendering. False: the word has no such meaning.

Set before the research began.

1. E1 Apocalypse - Etymology, Origin & Meaning - Etymonline Etymonline (Douglas Harper)

   “from Greek apokalyptein "uncover, disclose, reveal," from apo "off, away from" (see apo-) + kalyptein "to cover, conceal"”

2. E2 Greek New Testament Dictionary Bill Mounce (billmounce.com)

   “pr. uncover; to reveal, Mt. 11:25; pass. to be disclosed, Lk. 2:35”

3. E3 What the Bible says about Apocalypto Bible Tools (Forerunner Commentary, David C. Grabbe)

   “This noun comes from the verb apocalupto, which literally means "to take away the veil," such as when a painting or statue has its covering taken away.”

4. E4 What the Bible says about Apocalypto Bible Tools (Forerunner Commentary, David C. Grabbe)

   “Even though apocalypsis is most often translated "revelation," the best equivalent word in English is "unveiling."”

Etymonline traces 'apocalypse' to Greek apokalyptein, 'uncover, disclose, reveal', built from apo 'off' and kalyptein 'to cover, conceal' (E1). Mounce's New Testament dictionary marks 'uncover' as the proper (literal) sense of the verb apokalyptō, then gives 'reveal' (E2). A Bible commentary says the noun comes from the verb apocalupto, which literally means 'to take away the veil', and that the noun is most often translated 'revelation' (E3, E4). So the evidence supports 'unveiling' as the literal, etymological sense, with 'revelation' as the usual sense. That matches the mostly-true criterion. None of the sources is a full standard lexicon entry for the noun ἀποκάλυψις.