The most common and most likely answer to this crossword clue is the 7 letter word NEURONE
I've seen this crossword clue in The Times
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More clues leading to the result NEURONE
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The straight part
We know that "special cell" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case special cell = neurone.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 NEURONE mean?
NEURONE noun- A cell of the nervous system, which conducts nerve impulses; consisting of an axon and several dendrites. Neurons are connected by synapses.
- A nervure of an insect's wing.
- An artificial neuron (mathematical function serving as an essential unit of an artificial neural network)