The most common and most likely answer to this crossword clue is the 6 letter word ALEXIA
A
L
E
X
I
A
Buddy explains!
The straight part
We know that "speech disorder" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case speech disorder = alexia.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 ALEXIA mean?
ALEXIA noun- Word blindness, the inability, due to a cerebral disorder, to comprehend or understand writing.