第一 (だいいち)first; foremost; number one

first; foremost; number onenouns which may take the genitive case particle 'no', noun (common) (futsuumeishi)
most importantnouns which may take the genitive case particle 'no', noun (common) (futsuumeishi)
best; greatest; mostnouns which may take the genitive case particle 'no', noun (common) (futsuumeishi)
above all; besides; in any caseadverb (fukushi)

第一, its kanji, and other words that share them.Open this graph

Kanji in 第一

次第にしだいにgradually (progress into a state)
第一歩だいいっぽfirst step
第三者だいさんしゃthird party; third person
第一人者だいいちにんしゃleading person; foremost figure
第二次世界大戦だいにじせかいたいせんSecond World War; World War II
第一線だいいっせんthe front (of a battlefield); forefront
第一声だいいっせいfirst words said (e.g. when meeting someone); first thing out of one's mouth
第三国だいさんごくa third country
一つひとつone
一方いっぽうone (esp. of two); the other
一時いちじone o'clock
一月いちがつJanuary
一番いちばんnumber one; first
一般いっぱんgeneral; universal
一部いちぶone part; one portion
十一じゅういちeleven; 11

See how 第一 connects to the rest of Japanese.