Seems an implausible group all together (7)

I believe the answer is:

enmasse

I'm a little stuck... Click here to teach me more about this clue!

'all together' is the definition.
(I've seen this before)

'seems an implausible group' is the wordplay.
'seems an' anagrams to 'ENMASSE'.
However, I am unsure how the anagram is indicated.

Can you help me to learn more?

(Another definition for enmasse that I've seen is " All together".)

I've seen this clue in The Irish Times.

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