Step by model stressed indicator of former action (4,5)
I believe the answer is:
past tense
'indicator of former action' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'step by model stressed' is the wordplay.
'step' becomes 'pas' (I've seen this in another clue).
'by' is a charade indicator (letters next to each other).
'model' becomes 't' (Ford Model T car).
'stressed' becomes 'tense' (I've seen this in another clue).
'pas'+'t'+'tense'='PAST TENSE'
Can you help me to learn more?
(Other definitions for past tense that I've seen before include "Grammatical verb form" , "history?" , "Was perhaps" , "It expresses something that has happened" , "Form of verb that indicates time before the present" .)