The most common and most likely answer to this crossword clue is the 6 letter word FLUENT
I've seen this crossword clue in Financial Times
F
L
U
E
N
T
More clues leading to the result FLUENT
- Expert in tongue disease joining hospital department
- Easily flowing in pipe, not empty
- Complaint NHS department is well able to explain
- Free-flowing channel, not without content
- Competent books on orally transmitted infection
- Articulate head of faculty advanced round university
- Easy infection by hospital department
- Able to have a good time and suffer alternately
- Articulate complaint put in front of English heritage body
- Part of hospital goes on after illness without interruption
Buddy explains!

The straight part
We know that "well able to explain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case well able to explain = fluent.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 FLUENT mean?
FLUENT noun- A continuous variable, especially one with respect to time in Newton's Method of Fluxions.
- That flows; flowing, liquid.
- Able to use a language accurately, rapidly, and confidently – in a flowing way.