lumber, log, timber, wood, materials, ingredients, talent
材 centers on raw material with potential: lumber, timber, or wood as a physical substance, and by extension any ingredient or material that can be shaped into something useful. The talent sense is a natural metaphor for a person's raw ability waiting to be developed.
材 combines 木 (tree, wood) with 才, which likely contributes the sound and the idea of raw material or ability. The character originally referred to usable timber and later extended to materials and talent.
A tree (木) with potential (才) is lumber waiting to become something: 材 is raw material, whether wood or a person's talent.
For ザイ, imagine a lumberjack shouting 'ZAI!' as he chops a log: ZAI -> ザイ, and the log is raw timber.
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ingredient; (raw) material; resource
gathering material (for an article, novel, etc.); collecting information; covering (an event, incident, etc.); reporting; interview (for a news story)
materials; ingredients
capable person; talented person
wood; lumber; timber
foodstuff; ingredient
machinery and materials; equipment
teaching materials
subject; theme
(raw) material
lumber; timber; wood
raw materials; ingredients
material
outstanding talent; person of exceptional talent; gifted person
building material
wood (for building); lumber; timber
component; part; material; member
(building) stone
subject matter of a painting
steel material