The most common and most likely answer to this crossword clue is the 8 letter word MARGINAL
I've seen this crossword clue in Independent
M
A
R
G
I
N
A
L
More clues leading to the result MARGINAL
- Slight breaks alarming
- Alarming changes on the border
- Alarming changes in key election seat
- Alarming fractures on the outside
- Alarming, stumbling on the edge
- Alarming to be treated as almost irrelevant
- On the verge of alarming changes
- Unimportant constituency in The Borders
- Alarming changes on border
- Hotly contested seat alarming liberal
Buddy explains!

The straight part
We know that "triple definition?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case triple definition? = marginal.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 MARGINAL mean?
MARGINAL noun- Something that is marginal.
- A constituency won with a small margin.
- Of, relating to, or located at or near a margin or edge; also figurative usages of location and margin (edge).
- Determined by a small margin; having a salient characteristic determined by a small margin.
- Pertaining to changes resulting from a unit increase in production or consumption of a good.