The most common and most likely answer to this crossword clue is the 13 letter word HETEROGENEOUS
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result HETEROGENEOUS
Buddy explains!
The straight part
We know that "Unlike" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unlike = heterogeneous.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 HETEROGENEOUS mean?
HETEROGENEOUS adjective- Diverse in kind or nature; composed of diverse parts.
- Incommensurable because of different kinds.
- Having more than one phase (solid, liquid, gas) present in a system or process.
- Visibly consisting of different components.
- Of a network comprising different types of computers, potentially with vastly differing memory sizes, processing power and even basic underlying architecture; alternatively, of a data resource with multiple types of formats.