The most common and most likely answer to this crossword clue is the 12 letter word MONOSYLLABLE
I've seen this crossword clue in The Daily Telegraph
M
O
N
O
S
Y
L
L
A
B
L
E
More clues leading to the result MONOSYLLABLE
Buddy explains!
The straight part
We know that "‘Word’ for Mac but not Linux?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case ‘word’ for mac but not linux? = monosyllable.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 MONOSYLLABLE mean?
MONOSYLLABLE noun- A word of one syllable.
- A euphemism for the word cunt