The most common and most likely answer to this crossword clue is the 13 letter word LEXICOGRAPHER
I've seen this crossword clue in The Times
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More clues leading to the result LEXICOGRAPHER
Buddy explains!
The straight part
We know that "My career is meaningful by definition" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case my career is meaningful by definition = lexicographer.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 LEXICOGRAPHER mean?
LEXICOGRAPHER noun- One who writes or compiles a dictionary