Meaning of 一子 in Japanese

Definition of 一子

いっし(isshi) 【一子】

いっしそうでん(isshisouden) 【一子相伝】

(n) transmission of the secrets of an art, craft, trade or learning from father to only one child
一子相伝の技と言うわりには、彼の蹴りは大した事はないね。
For a guy who was chosen by his father as the only son to be taught the secrets of this martial art, he doesn't have much of a kick.

だいいっし(daiisshi) 【第一子】

一子ちゃんは同じ穴のムジナおなじあなのムジナか、同輩どうはいの親しみしたしみを込めた笑みえみを俺おれに向けるむける。

I guess Ichiko is a fellow rule-breaker, she's sending me a smile filled with affection for a comrade.

去年第一だいいち子こを出産しゅっさんしましたする。

I delivered my first child last year.

一子相伝いっしそうでんの技と言うわりには、彼かれの蹴りけりは大したたいした事ことはないね。

For a guy who was chosen by his father as the only son to be taught the secrets of this martial art, he doesn't have much of a kick.