in Colossians 4:10 denotes a "cousin" rather than a nephew (AV, "sister's son"). "Cousin" is its meaning in various periods of Greek writers. In this sense it is used in the Sept., in Numbers 36:11 . In later writings it denotes a nephew; hence the AV rendering. As Lightfoot says, there is no reason to suppose that the Apostle would have used it in any other than its proper sense. We are to understand, therefore, that Mark was the cousin of Barnabas. See SISTER.

2: συγγενής

(Strong's #4773 — Adjective — sungenis — soong-ghen-ace' )

in Luke 1:36 (so in the most authentic mss.) and sungenes in Luke 1:58 (plural), AV, "cousin" and "cousins," respectively signify "kinswoman" and "kinsfolk," (RV); so the RV and AV in Luke 2:44; 21:16 . The word lit. signifies "born with," i.e., of the same stock, or descent; hence "kinsman, kindred." See KIN , KINSFOLK , KINSWOMAN.

Bibliography Information
Vines, W. E., M. A. Entry for 'Cousin'. Vine's Expository Dictionary of NT Words. https://www.studylight.org/dictionaries/eng/ved/c/cousin.html. 1940.

Bible Dictionaries Cousin

Vine's Expository Dictionary of NT Words

Bible Dictionaries
Cousin