Hammers would be present, but not always saw (5)
I believe the answer is:
tense
'saw' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
I can't explain the rest of the clue.
(Other definitions for tense that I've seen before include "Nervous or tight" , "under pressure" , "In a nervous state" , "Anxious - future, perhaps?" , "Verb form indicating time" .)