I am just a beginner, and I am reading Tae Kim's Guide to Japanese. My questions are:
Why is the past tense of 登録, 登録した?
Is 登録 (register) a noun or a verb?
In the following example, the word should be a verb, right? If it is a verb, it is ru-verb or u-verb? メールアドレスを登録した。 Registered email address.
(This question is not related to any questions above and the topic) By the way, what is the best English-Japanese dictionary? Also, how can I know if a word is a noun, i-adjective, na-adjective, u-verb, ru-verb, or an exception?