Herder: 'Say nothing terribly deep or grand, initially' (8)

I believe the answer is:

sheepdog

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'herder' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.

'say nothing terribly deep or grand initially' is the wordplay.
'say nothing' becomes 'sh' (I've seen this in other clues).
'terribly' is an anagram indicator.
'initially' suggests taking the first letters.
The initial letters of 'or grand' is 'og'.
'deep' anagrammed gives 'eepd'.
'sh'+'eepd'+'og'='SHEEPDOG'

Can you help me to learn more?

(Other definitions for sheepdog that I've seen before include "Pastoral assistant?" , "Working farm animal" , "eg Border collie" , "could it be Old English?" , "Farmer's herding helper" .)

I've seen this clue in The Guardian.

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