Living together in company with sixteen? Extraordinarily tense (10)

'living together' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?

'company with sixteen? extraordinarily tense' is the wordplay.
'company' becomes 'co' (abbreviation).
'with' means one lot of letters go next to another.
'extraordinarily' is an anagram indicator.
'tense' becomes 't' (abbreviation used in many dictionaries).
'sixteen' with letters rearranged gives 'existen'.
'co'+'existen'+'t'='COEXISTENT'

'in' acts as a link.

Can you help me to learn more?