younger male cousin
Specifically a male cousin who is younger than the speaker. The reading いとこ is a jukujikun; the on'yomi reading じゅうてい is rare and mostly found in formal or written contexts.
See also: 従兄
My younger male cousin is a university student.
夏休みに従弟が遊びに来た。
My younger male cousin came to visit during summer vacation.
従兄 refers to an older male cousin, while 従弟 refers to a younger male cousin.
younger male second cousin
Kanji spelling specifically for a younger male cousin. The reading いとこ is a jukujikun.
The kanji 従 means 'follow' or 'obey', and 弟 means 'younger brother', together indicating a younger male relative in the same generation. The reading いとこ is a jukujikun, a native Japanese word assigned to these kanji.