The status of Armenian as a Satem language as opposed to a Centum language with secondary assibilation rests on the evidence of a very few words.
From the en.wikipedia.org
For instance, it is known that the assibilation found in French and Swedish were later developments as linguists have extensive documentation of Latin and Old Swedish.
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As a result, it is sometimes difficult to firmly establish which languages were part of the original Satem diffusion and which were affected by secondary assibilation in a later time period.
From the en.wikipedia.org
More examples
The development of a consonant phoneme into a sibilant
Sibilation: pronunciation with a sibilant (hissing or whistling) sound
(assibilate) insert a sibilant sound before or after (another sound)
In linguistics, assibilation is the term for a sound change resulting in a sibilant consonant. It is commonly the final phase of palatalization.
(assibilated) Articulated as a sibilant: /r/ is so articulated (approximating to [z]) in a number of dialects.