then why does greek have a word for cousin?
ἀνεψιός, -οῦ, ὁ, [for ἁ-νεπτ-ιός con-nepot-ius, cf. Lat. nepos, Germ. nichte, Eng. nephew, niece; Curtius § 342], a cousin: Col. 4:10. (Num. 36:11; Tob. 7:2.) [Cf. Lob. ad Phryn. p. 306; but esp. Bp. Lghtft. on Col. l. c.; also B. D. Am. ed. s. v. Sister’s Son.]*
Thayer, J. H. (1889). A Greek-English lexicon of the New Testament: Being Grimm's Wilke's Clavis Novi Testamenti (45). New York: Harper & Brothers.
ἀνεψιός, ὁ, a first-cousin, cousin, Il., Hdt., Att.
2. a nephew, Hdt. [When the ult. is long, Hom. lengthens also the penult., ἀνεψῑοῦ κταμένοιο.] (From α euphon. or copul., and ΝΕΠ, whence also Lat. nepos, neptis.)
Liddell, H. (1996). A lexicon : Abridged from Liddell and Scott's Greek-English lexicon (69). Oak Harbor, WA: Logos Research Systems, Inc.
ἀνεψιός 431
This word, which in Greek writers is regularly applied to cousins german whether on the father’s or on the mother’s side
Moulton, J. H., & Milligan, G. (1930). The vocabulary of the Greek Testament (42). London: Hodder and Stoughton.
Seems like the word cousin was well known to greek writters of the time!