Out of place, one communication that's understandable (10)
I believe the answer is:
explicable
'understandable' is the definition.
(synonyms)
'out of place one communication' is the wordplay.
I cannot quite understand how this works, but
'place' could be 'pl' (abbreviation used in postal addresses) and 'pl' is present in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'communication' could be 'cable' (cable is a kind of communication) and 'cable' is present in the answer.
'out of' could be 'ex' ('out of' in Latin) and 'ex' is located in the answer.
No letters remain.
This explanation may well be incorrect...
'that's' acts as a link.
Can you help me to learn more?
(Another definition for explicable that I've seen is " readily understood".)