The most common and most likely answer to this crossword clue is the 12 letter word SMALLHOLDING
I've seen this crossword clue in The Daily Telegraph
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Buddy explains!
The straight part
We know that "One taking this one won’t gain much ground" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one taking this one won’t gain much ground = smallholding.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 SMALLHOLDING mean?
SMALLHOLDING noun- A piece of land, smaller than a farm, used for the cultivation of vegetables or the breeding of animals.
- A small plantation or land with a small number of slaves (generally 19 or less). Contrasted with middling plantation (20-49 slaves) and large plantation (50+ and owned by planters).