The most common and most likely answer to this crossword clue is the 9 letter word MONOTONIC
I've seen this crossword clue in The Guardian
M
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N
O
T
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Buddy explains!
The straight part
We know that "lacking variety" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lacking variety = monotonic.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 MONOTONIC mean?
MONOTONIC adjective- Of or using the Greek system of diacritics which discards the breathings and employs a single accent to indicate stress. It replaced polytonic system in 1982.
- Said of a function that either never decreases or never increases as its independent variable increases.
- Uttered in a monotone; monotonous.