a father's brother: a man's paternal uncle, or by extension a near male relative on the father's side
In the law and the histories this is a precise family word: the brother of one's father, the closest male kin after father and brother. It marks the man who carries weight in the clan as protector, provider, and redeemer. Leviticus 18:14 spells it out by naming the same person two ways in one breath, your father's brother and your uncle, so the meaning is not in doubt.
The word anchors a chain of family duty. In the redemption laws it names the rung just past brother, the relative obligated to buy back a poor kinsman or his land (Leviticus 25:49); add son to it and you get the first cousin, the daughters of Zelophehad marrying their cousins to keep the inheritance in the father's line (Numbers 36:11). The same word fixes Esther as Mordecai's cousin, not his niece, since she is the daughter of his uncle.
The boundary is the father's side. Hebrew uses this word for the paternal uncle and keeps it there; it does not reach across to the mother's brother or to relatives outside the father's line. In a few places, especially the funeral scene of Amos 6:10 and the purchase in Jeremiah 32, it loosens to a wider near relative, but always within that paternal, duty-bound family circle.