This reminds me of an OotS comic about the word "level" and how many problems in DnD would have been solved if someone at TSR had bought a thesaurus.
It's actually got a section in the (first edition) AD&D Players Handbook:
An Explanation of the Usages of the Term "level": The term level has multiple meanings in this game system. Although substitute terminology could have been used in ADVANCED DUNGEONS & DRAGONS, common usage of the term level to include multiple meanings is prevalent amongst existing players, so the term has been retained herein. The usages for level are:
1. Level as an indication of Character power: A player character begins the game at 1st level, i.e. the lowest possible level for a player character. The higher the level number, the more powerful the character is.
2. Level as used to indicate the depth of the dungeon complex beneath the ground: The 1st level of a dungeon is the first layer of the underground complex of tunnels, passages, rooms, chambers, and so forth. It is the 1st level beneath the ground. Beneath the 1st level is the 2nd, below that is the 3rd. 4th, Sth, etc. The higher the number, the lower the dungeon level (and the more hazardous its perils).
3. Level as a measure of magic spell difficulty: The magic spells available to some classes of characters are graded by difficulty factor - which, incidentally, reflects the spells' effectiveness to some extent. 1st level spells are the basic ones available to beginning characters. They are generally the least powerful spells. Next come 2nd level spells, then come 3rd level spells, and so on. The highest level of any type of magic spell is 9th level, spells usable only by 18th level magic-users - lesser magic-users can possibly employ such spells under certain circumstances which are explained hereafter, but only at considerable risk.
4. Level as a gauge of a "monster's'' potential threat: Relatively weak creatures, monsters with few hit points, limited or non-existent magical abilities, those which do little damage when attacking, and those which have weak, or totally lack, venom are grouped together and called 1st level monsters. Slightly more powerful creatures are ordered into 2nd level, then comes 3rd. 4th, 5th, and so on all the way up to 10th level (the highest, which includes the greatest monsters, demon princes, etc.).
It was initially contemplated to term character power as rank, spell complexity was to be termed power, and monster strength was to be termed as order. Thus, instead of a 9th level character encountering a 7th level monster on the 8th dungeon level and attacking it with a 4th level spell, the terminology would have been: A 9th rank character encountered a 7th order monster on the 8th (dungeon) level and attacked it with a 4th power spell. However, because of existing usage, level is retained throughout with all four meanings, and it is not as confusing as it may now seem.
Cheers!