The most common and most likely answer to this crossword clue is the 4 letter word SIRE
I've seen this crossword clue in Independent
S
I
R
E
More clues leading to the result SIRE
- Father and son put on payroll in Bow
- Father is up and about
- Father beginning to show anger
- Father Christmas, I remembered stocking?
- Father sounds like one moaning aloud
- Longing, to some extent, for father
- Father is around and about
- Father and husband leaving county
- Son with passion to become a gentleman
- Hard to leave county and old address
Buddy explains!

The straight part
We know that "a gentleman" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a gentleman = sire.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 SIRE mean?
SIRE noun- A lord, master, or other person in authority, most commonly used vocatively: formerly in speaking to elders and superiors, later only when addressing a sovereign.
- A male animal; a stud, especially a horse or dog, that has fathered another.
- A father; the head of a family; the husband.
- A creator; a maker; an author; an originator.
- (of a male) to procreate; to father, beget, impregnate.