Difficult puzzle is almost excessively huge one to crack (7)
I believe the answer is:
toughie
'difficult puzzle' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'almost excessively huge one to crack' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'excessively' becomes 'too' (to too great a degree).
'one' becomes 'i' (Roman numeral).
'to crack' indicates an anagram (I've seen 'cracked' mean this).
'too' with its final letter taken off is 'to'.
'huge'+'i'='hugei'
'hugei' anagrammed gives 'ughie'.
'to'+'ughie'='TOUGHIE'
'is' is the link.
Can you help me to learn more?
(Other definitions for toughie that I've seen before include "A difficult test" , "DT's new difficult crossword" , "Difficult problem" , "poser" , "It may prove impossible" .)