Is there a difference between "yon sel" and "yon sel grenn"?

Both basically mean "only one".
sèl adj. → alone, only, individual, single
yon grenn → one

yon sèl (one)
yon sèl grenn (a single one)
yon grenn (one)
youn (one)
youn sèlman (just one)
One, only one, just one

1. Eske w gen youn ou ka prete'm?
    Do you have one that you can lend to me?

2. Mwen rete yon sèl grenn plim nan ki rete.  Mwen p'ap ka prete w li.
    I have a single pen left.  I can't loan it to you.

3. Mwen razè jodi a. Mwen gen yon sèl gren dola nan pòch mwen.
    I am broke today.  I have one single dollar in my pocket.

4.  Podyab madan Paul.  Yon sèl grenn pitit la li genyen, l'ale nan lagè, li pa tounen.
     Poor Mrs. Paul.  Her only child went to war and did not come back.

5.  Mwen youn sèlman.
     I have just one.

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