1.
many, much, numerous
Large in number or amount. The opposite of 少ない (すくない - few). Used for both countable and uncountable things.
多い conjugates as an i-adjective: 多くない (negative), 多くて (te-form), 多かった (past). Important: 多い usually cannot directly modify nouns (× 多い人). Instead, say 人が多い or use たくさんの. However, 多くの (おおくの - many) can modify nouns: 多くの人 (many people).