Tome (魔道書 lit. Grimoire) is a general term for magical weapons, excluding Staves.
Tomes are spellbooks that function as weapons for mages and similar offense-focused magic classes. They appear in most every Fire Emblem title save for Fire Emblem Gaiden, its remake, and Three Houses, which use magic systems not reliant on tomes.
In Fire Emblem: Mystery of the Emblem (and by extension Fire Emblem: Shadow Dragon and the Blade of Light), tomes and staves are created by focusing energy into them then using it from the object freely.
In the later games Fire Emblem: Path of Radiance and Fire Emblem: Radiant Dawn, it is stated in several instances that tomes are written in 'Old Speech', the original language of the continent these games take place on, Tellius. Old Speech is not mentioned in any other Fire Emblem games, however, a few games state that tomes are written in a lost ancient language. A few characters in Path of Radiance and Radiant Dawn can speak Old Speech, most notably the Heron laguz.
Tomes are used to cast magical attacks. They usually weigh very little to reflect the low strength of magic users. In the GBA titles there were three types of tomes: Anima, Dark, and Light. These three types of magic form a triangle similar to the Weapon Triangle, known as the Trinity of Magic: Anima beats Light, Light beats Dark, and Dark beats Anima.
In Path of Radiance, Anima magic was further divided into three separate magic classes (Wind, Fire, and Thunder) which form the Anima Triangle: Fire beats Wind, Wind beats Thunder, and Thunder beats Fire. Many new tomes were created for each of these classes. As a result, Dark magic was completely removed so as not to overwhelm the player with too many spells. Light magic is still present in this game, however, unlike in the earlier games, it is neutral against Anima (and vice versa).
In Radiant Dawn, the original magic triangle returned alongside the newer Anima triangle. Dark magic is effective against all three types of Anima magic, which are in turn effective against Light magic.
In Fire Emblem Awakening, only Anima and Dark magic exists and no light magic exists, except for Book of Naga. No form of the magic triangle exists in the game meaning all tomes deals neutral damage to other tome wielding units.
In Fates, a new type of weapon is introduced as the Hoshidan counterpart of the traditional Tomes that are used in Nohr. They are known as Scrolls (呪 lit. Spells), and instead of invoking the elements, Scrolls summon ancient spirits to attack enemies, with the animals of the first ten earth branches of the Chinese Zodiac forming the main hierarchy. Scrolls take the form of long, thin pieces of wood with magic symbols inscribed onto them, and are bundled in groups of four or eight. More expensive Scrolls are known to be manufactured from higher-grade materials and embellished with more decorations.
The most dramatic change made to magic and tome use in Fire Emblem Fates is the game's revised weapon triangle. Magic is grouped with swords, making all tomes strong against axes and bows, but weak against lances and shuriken.
In Fire Emblem Heroes, tomes have undergone yet another restructuring. Dark, Light, and Anima tomes are consolidated into Red, Blue, Green tomes, which correspond to swords, lances, and axes respectively. Fire and Dark tomes are typically Red. Wind tomes are typically Green. Thunder tomes are typically Blue. Light tomes are both Green and Blue. Anima mages that had no previous elemental affiliation (such as Nino and Lilina) are assigned an arbitrary element.
In the action game spin-off Fire Emblem Warriors and Fire Emblem Warriors: Three Hopes, the majority of the tomes that appear do not conform to traditional anima relationship or light/dark magic. The strength of these tomes are based on the metal-based ranking of other weapon types, such as the Bronze Tome and Iron Tome. There are also unique tomes based on those found in other games, such as Moonlight and Brynhildr in Fire Emblem Fates.
The term 'Tome' is an archaic English word literally meaning 'book'.