The most common and most likely answer to this crossword clue is the 6 letter word LINEAL
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More clues leading to the result LINEAL
- Direct telephone connection with Alabama
- It’s true about one small number of legitimate descent
- Like an ancestor occupying hovel in Ealing
- From father to son, all in ecstasy perhaps
- Alien life, originally evolving from the same ancestor
- Looking back, not even one royalis of direct descent
- Hereditary business by a learner
- Direct approach's often manly
- Faithful about family king abandoned, marking direct descent
Buddy explains!

The straight part
We know that "marking direct descent" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case marking direct descent = lineal.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does LINEAL mean?
LINEAL adjective- (family) Of a family relationship that includes mothers, fathers, daughters, sons, grandparents, grandchildren, etc., but not siblings; as opposed to collateral.
- Inheriting by direct descent; having the right by direct descent to succeed (to).
- Composed of lines; delineated.
- In the direction of a line; of a line; of or relating to a line; measured on, or ascertained by, a line; linear.