The most common and most likely answer to this crossword clue is the 5 plus 6 letter word BIRTH WEIGHT
I've seen this crossword clue in Independent
B
I
R
T
H
W
E
I
G
H
T
Buddy explains!
The straight part
We know that "Ten pounds perhaps for a big delivery?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ten pounds perhaps for a big delivery? = birth weight.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.