The most common and most likely answer to this crossword clue is the 9 letter word ASSEMBLER
I've seen this crossword clue in Independent
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More clues leading to the result ASSEMBLER
Buddy explains!
The straight part
We know that "One who puts together" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one who puts together = assembler.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 ASSEMBLER mean?
ASSEMBLER noun- A program that reads source code written in assembly language and produces executable machine code, possibly together with information needed by linkers, debuggers and other tools.
- Assembly language.
- One who assembles items.
- A nanodevice capable of assembling nanodevices, possibly including copies of itself, according to a plan.